Pharmacology & Therapeutics

Home , Adrenergic antagonist, Amesergide, Emily Colas, Neuroendocrine cell

Pharmacology & Therapeutics 170 (2017) 14–36

Contents lists available at ScienceDirect

journal homepage: www.elsevier.com/locate/pharmthera

Associate editor: N. Frossard

New therapeutic opportunities for 5-HT2 receptor ligands Luc Maroteaux b,1, Estelle Ayme-Dietrich a,1, Gaëlle Aubertin-Kirch a, Sophie Banas b, Emily Quentin b, Roland Lawson a, Laurent Monassier a,⁎ a Laboratoire de Neurobiologie et Pharmacologie Cardiovasculaire EA7296, Faculté de Médecine, Fédération de Médecine Translationnelle de Strasbourg, Université et Centre Hospitalier de Strasbourg, Strasbourg, France b INSERM UMR S-839, Institut du Fer à Moulin, Université Pierre et Marie Curie, 17 rue du Fer à Moulin 75005, Paris, France article info abstract

Available online 19 October 2016 Serotonergic dysfunction is mainly associated with neuropsychiatric and cardiovascular disorders but has also been linked with many other pathological conditions. Serotonin (5-hydroxytryptamine, 5-HT) mediates numer- Keywords: ous physiological functions in the brain and the periphery by activating a variety of receptors. 5-HT receptors are 5-HT2 receptors divided into four classes, three of which belong to the G protein-coupled receptor family. This review provides Selectivity an overview of the recent pharmacological developments involving the Gq-coupled 5-HT2 receptor subfamily Pathological function as well as the pathological implications of this receptor subfamily with regard to ﬁbrosis, the central nervous Therapeutic track system, cardiovascular disorders, and cancer. The ﬁnal section highlights new therapeutic opportunities and emerging research revealing unexplored medical opportunities for this class of 5-HT receptors. The development

of biased 5-HT2 receptor ligands appears to be an interesting topic in various areas. In light of recent discoveries, the need for the development of new and safer drugs should take into account the risk of cardiovascular side effects such as pulmonary hypertension and heart valve disease. © 2016 Elsevier Inc. All rights reserved.

Contents

1. Introduction...... 14

2. 5-HT2 receptors: structure, coupling, oligomerization, selective ligands, allosteric modulators, biased agonists . 15

3. Pathologies and 5-HT2 receptors...... 18 4. Emergingresearchandnewtherapeuticopportunities...... 28 5. Conclusionsandprospects...... 31 Conﬂictofinterest...... 31 Acknowledgments...... 31 References...... 31

1. Introduction et al. (1988) was the ﬁrst to report the cloning of a full-length functional

serotonin receptor from rat (the 5-HT1c receptor), this publication was This review focuses on three serotonin (5-hydroxytryptamine, shortly followed by considerable efforts from several groups that cloned

5-HT) receptors belonging to the 5-HT2 receptor subfamily: the other unidentiﬁed 5-HT receptors. The classical 5-HT2 receptor de- 5-HT2A, 5-HT2B, and 5-HT2C subtypes. Although the work by Julius scribed by Peroutka et al. (1981) was cloned from rats slightly later in 1988 (Pritchett et al., 1988) followed by human analogue (Branchek

et al., 1990; Saltzman et al., 1991) and was renamed 5-HT2A.The 5-HT1c receptor was renamed 5-HT2C because of its structural similarity ⁎ Corresponding author at: LaboratoiredeNeurobiologieetPharmacologie to the other 5-HT2 receptor, identical second messenger pathways, and Cardiovasculaire, Faculté de Médecine, Université et Centre Hospitalier de Strasbourg, similar pharmacological properties. Pharmacological studies attempting 11 rue Humann, 67085 Strasbourg, France. Tel.: +33 368853392; fax: +33 368853388. to characterize the contractile serotonergic receptor in the rat stomach E-mail address: [email protected] (L. Monassier). 1 Luc Maroteaux and Estelle Ayme-Dietrich contributed equally to this review and are fundus initially documented its similarity to the 5-HT2C receptor. considered co-authors. Despite the absence of detectable 5-HT2C receptor mRNA in the rat

http://dx.doi.org/10.1016/j.pharmthera.2016.10.008 0163-7258/© 2016 Elsevier Inc. All rights reserved. L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36 15 stomach fundus, only homology cloning permitted the identification of 2.2. Selective agonists a new receptor in 1992 in rat and mouse that was named 5-HT2B (Foguet et al., 1992a, 1992b; Kursar et al., 1992; Loric et al., 1992; There is virtually no highly selective agonist for a particular 5-HT2 Wainscott et al., 1993) and in 1994 in humans (Choi et al., 1994; receptor: Kursar et al., 1994; Schmuck et al., 1994; Wainscott et al., 1996). - BW723C86: 1-methyl-2-[5-(2-thienylmethoxy)-1H-indole-3-yl] The investigation of the contribution of these three 5-HT2 receptors ethylamine hydrochloride has been reported to have 10-fold selec- in mammalian physiology has led to a large number of reports in nearly tivity over the human 5-HT and 100-fold selectivity over the all functions and organs. Some selective compounds stimulating or 2C 5-HT receptors (Porter et al., 1999; Jerman et al., 2001; Knight blocking these receptors provided an opportunity to explore various 2A et al., 2004; Cussac et al., 2008). Lorcaserin [(1R)-8-chloro-2,3,4,5- areas of human diseases. In this review, we will emphasize some impor- tetrahydro-1-methyl-1H-3 benzazepine] has approximately 10- tant aspects of the cellular and molecular biology of these receptors and fold higher affinity for 5-HT receptor (Thomsen et al., 2008) over highlight some clinical situations in which these receptors appear as 2C the 5-HT and 5-HT receptors. pathophysiological cornerstones. 2A 2B - Nor-dexfenfluramine (a metabolite of dexfenfluramine), methylergonovine (a metabolite of methysergide), and Ro 60-0175: 2(S)-1- (6-chloro-5-fluoro-1H-indol-1-yl)-2-propanamine fumarate are all 2. 5-HT2 receptors: structure, coupling, oligomerization, preferential 5-HT agonists with approximately 10-fold selectivity selective ligands, allosteric modulators, biased agonists 2B over the 5-HT2C receptor (Cussac et al., 2002). - 2,5-dimethoxy-4-iodoamphetamine (DOI) is a non-selective nearly The closely related 5-HT2 receptors are members of the rhodopsin full agonist at 5-HT receptors with similar affinity to the 5-HT , family of G protein-coupled receptors (GPCRs) that activate multiple 2 2A 5-HT ,and5-HT receptors (Porter et al., 1999; Jerman et al., intracellular signalling networks. The classical signal transduction path- 2B 2C 2001; Knight et al., 2004; Cussac et al., 2008). way for this subfamily is the Gq/11-coupled activation of phospholipase - Alpha-methyl-5-HT is a non-selective nearly full agonist at 5-HT2 C (PLC), although these 5-HT2 receptors can also activate phospholipase receptors with a similar affinity towards the 5-HT ,5-HT ,and D and phospholipase A2 by interacting with additional pathways. These 2A 2B 5-HT2C receptors (Porter et al., 1999; Jerman et al., 2001; Knight 5-HT2A, 5-HT2B, and 5-HT2C receptors are post-transcriptionally modi- et al., 2004). fied by alternative RNA splicing, a common mechanism for achieving protein diversity. RNA editing, on the other hand, is a less common process for generating molecular diversity. In fact, the 5-HT2C receptor 2.3. Selective antagonists is one of the few GPCRs known to be edited. RNA editing of the 5-HT2C receptor generates functionally distinct protein variants by altering A few selective antagonists are available for the 5-HT2 receptor the genetic code at the mRNA level. subtypes:

-Theﬁrst highly selective 5-HT2A receptor antagonist reported 2.1. Structure was MDL100907 [(R)-(+)-α-(2,3-dimethoxyphenyl)-1-[2-(4- ﬂuorophenylethyl)]-4-piperidine-methanol] (Knight et al., 2004).

5-HT2 receptors are 7 transmembrane domain receptors with fairly Sarpogrelate [succinic acid mono-(1-dimethylaminomethyl-2-(2- long extracellular N-terminal loops ranging from 55 amino acids for [2-(3-methoxyphenyl) ethyl] phenoxy) ethyl) ester hydrochloride], the human 5-HT2B and 5-HT2C receptors to 75 amino acids for the SR46349B [4-((3Z)-3-(2-dimethylaminoethyl)oxyimino-3-(2- human 5-HT2A receptor and an intracellular C-terminus ranging from fluorophenyl)propen-1-yl)phenol hemifumarate], and ketanserin 85 amino acids for the human 5-HT2B receptor to 75 amino acids for [3-[2-[4-(4-fluorobenzoyl)piperidin-1-yl]ethyl]quinazoline-2,4(1H, the human 5-HT2A and 5-HT2C receptors. A new and unanticipated 3H)-dione] are preferential 5-HT2A receptor antagonists with a 10- role of the 5-HT2B receptor N-terminus as a negative modulator affect- fold higher affinity over the 5-HT2C and/or 5-HT2B sites. ing both constitutive and agonist-stimulated activity of the receptor - The first highly selective 5-HT2B receptor antagonist reported was has been shown (Belmer et al., 2014). The recently published crystal LY266097: 1-(2-chloro-3,4-dimethoxybenzyl)-6-methyl-1,2,3,4- structure of the 5-HT2B receptor bound to ergotamine showed that tetrahydro-9H-pyrido[3,4-b]indole hydrochloride, with a pKi of 9.7 this receptor exhibits conformational characteristics in both the active for the human cloned 5-HT2B receptor and a 100-fold greater selec- and inactive states: an active-like state in the helix VII conformation of tivity over human 5-HT2C and 5-HT2A receptors (Audia et al., 1996). the 5-HT2B receptor but only partial changes in helix VI. The differential SB204741: N-(1-methyl-5-indolyl)-N′-(3-methyl-5-isothiazolyl) signalling patterns were also mirrored in the crystal structures, which urea has been reported as a selective 5-HT2B receptor antagonist showed features of a β-arrestin-biased activation state for the 5-HT2B with approximately 100-fold selectivity over the 5-HT2C and 5- receptor (Wacker et al., 2013; Wang et al., 2013). A likely structural HT2A receptors but with a low potency (Ki approximately 100 nM) explanation for the distinct conformational features and biased pharma- (Bonhaus et al., 1995). The tetrahydro-β-carboline LY272015 cology of ergotamine for 5-HT2B receptors can be found in the region of [6-chloro-5-methyl-N-(5-quinolinyl)-2,3-dihydro-1H-indole-1- the extracellular loop 2 (ECL2) junction with helix V (E212-R213-F214), carboxamide] is also a fairly selective and highly potent antagonist which forms an additional helical turn stabilized by a structured water (Cohen et al., 1996). RS127445 [2-amino-4-(4-fluoronaphth-1-yl)- molecule at the extracellular tip of helix V. The segment of ECL2 6-isopropylpyrimidine] was found to have sub-nanomolar affinity connecting helices III and V via the conserved disulphide bond is short- for the 5-HT2B receptor (pKi = 9.5) and 1000-fold selectivity for ened in the 5-HT2B receptor and creates a conformational constraint on this receptor compared to numerous other receptor and ion channel the position of the extracellular tip of helix V (Martí-Solano et al., 2014). binding sites and appears as the most selective, high-affinity 5-HT2B However, this structured water molecule involved in the ECL2 junction receptor antagonist currently available (Bonhaus et al., 1999). with helix V has been challenged since differential interactions of ergot- SB215505 [6-chloro-5-methyl-N-(5-quinolinyl)-2,3-dihydro-1H- amine with the top of helices V and VI could determine the rotational indole-1-carboxamide] behaves as a high-affinity and preferential freedom of helix VI (Liu et al., 2013). No crystal structures have reported inverse agonist at 5-HT2B receptors (Reavill et al., 1999). yet for the 5-HT2A or 5-HT2C receptors. - SB242084 [6-chloro-5-methyl-1-[6-(2-methylpyridin-3-yloxy) More work is needed to precisely understand the structure and func- pyridin-3-yl-carbamoyl]indoline] and RS-102221 [N-[5-[5-(2,5- tion of these receptors as well as their specificproperties. dioxo-spiro[imidazolidine-4,4′-piperidin]-1′-yl)pentanoyl]-2,4- 16 L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36

dimethoxy-phenyl]-4-(triﬂuoromethyl)benzenesulfonamide] 2.4. Coupling

are selective 5-HT2C antagonists (Bonhaus et al., 1997; Knight et al., 2004). Intracellular signals are inherently challenging targets because they - SB206553 [5-methyl-N-(3-pyridyl)-1,2,3,5-tetrahydrobenzo[1,2- are often ubiquitous; indeed, drug vectorization comes from GPCRs

b:4,5-b′]dipyrrole-1-carboxamide] is a mixed 5-HT2C/5-HT2B recep- not transduction pathways. Nonetheless, multi-target drugs acting tor antagonist. It has been reported as a selective 5-HT2C/2B receptor at two key nodes in a signalling network offer one answer. Another inverse agonist with 50- to 100-fold lower afﬁnity for 5-HT2A and approach to this concept is the manipulation of interactions between other sites (Kennett et al., 1996; Knight et al., 2004). 5-HT receptors and their protein partners. One good example is the

use of small peptides to decouple 5-HT2C receptors from their PDZ partners, which mimics the desensitization elicited by antidepressants

Non-selective 5-HT2 receptor antagonists such as ritanserin and (Gavarini et al., 2006). Conversely, blocking the interactions between mesulergine block 5-HT2 receptor-mediated effects. Atypical antipsy- 5-HT2C receptors and the phosphatase PTEN (phosphatase with tensin chotics including clozapine, asenapine, or cariprazine also have a fairly homology) reproduces the 5-HT2C agonist-induced inhibition of the ex- high afﬁnity for all 5-HT2 receptors (Wainscott et al., 1996; Millan citation of mesolimbic dopaminergic neurons by cannabinoids, thereby et al., 2003; Shahid et al., 2009; Kiss et al., 2010). Aripiprazole (OPC- preventing their rewarding effects (Ji et al., 2006). Hence, interference

14597) is a novel atypical antipsychotic drug that has higher antagonist with the association between 5-HT2C receptors and PTEN might be an activity (EC50 = 11 nM) at the human 5-HT2B receptor than at the interesting way to counteract drug addiction. 5-HT2A or 5-HT2C receptors (Shapiro et al., 2003). See Table 1 and the β-Arrestins direct the agonist-induced internalization of 5-HT PDSP database, http://kidbdev.med.unc.edu/databases/pdsp.php. receptors; however, agonist-independent association with β-arrestins

Table 1 (Cussac et al., 2002; Rashid et al., 2003; Shapiro et al., 2003; Knight et al., 2004; Rosenzweig-Lipson et al., 2006; Siuciak et al., 2007; Cussac et al., 2008; Thomsen et al., 2008; Shahid et al., 2009; Banas et al., 2011).

h5-HT2A r5-HT2A h5-HT2B r5-HT2B m5-HT2B h5-HT2C r5-HT2C m5-HT2C pKi pKi pKi pKi pKi pKi pki pKi

BW723C86 Banas, 2011, h2CINI, m2CVNi 7.89 ± 0.01 8.04 ± 0.15 6.90 ± 0.01 6.78 ± 0.05

Knight 2004 h2CINI 7.2 ± 0.08 7.33 ± 0.03 7.11 ± 0.21

Cussac 2008 h2CVSV 6.63 ± 0.06 7.85 ± 0.11 7.11 ± 0.01

RO600175 Banas, 2011, h2CINI, m2CVNi 9.01 ± 0.13 8.64 ± 0.14 7.72 ± 0.22 7.35 ± 0.29

Knight 2004 h2CINI 7.44 ± 0.04 8.27 ± 0.06 8.22 ± 0.29

Cussac 2008 h2CVSV 6.80 ± 0.08 8.66 ± 0.13 7.67 ± 0.07

WAY161503 Banas, 2011, h2CINI, m2CVNi 7.28 ± 0.19 7.84 ± 0.12 7.46 ± 0.05 6.92 ± 0.11

Rosenzweig 2006 h2C? 7.74 ± 0.11 7.22 ± 0.03 8.48 ± 0.14

CP809101 Siuciak 2C? 8.22 ± 0.15 7.19 ± 0.25 8.80 ± 0.11

Banas, 2011, h2CINI, m2CVNi 7.86 ± 0.18 8.41 ± 0.18 8.35 ± 0.02 7.72 ± 0.15

DOI Banas, 2011, h2CINI, m2CVNi 8.29 ± 0.18 7.87 ± 0.06 7.60 ± 0.02 7.41 ± 0.24

Knight 2004 h2CINI 9.02 ± 0.11 7.55 ± 0.05 8.08 ± 011

Cussac 2008 h2CVSV 8.04 ± 0.05 7.78 ± 0.09 7.73 ± 0.04

Norfenﬂuramine Banas, 2011, h2CINI, m2CVNi 8.02 ± 0.19 6.76 ± 0.23 7.09 ± 0.62 6.21 ± 0.07

Knight 2004 h2CINI 6.82 ± 0.29 7.00 ± 0.06 7.29 ± 0.04

D-LSD Knight 2004 h2CINI 9.12 ± 0.06 9.01 ± 0.09 8.96 ± 0.06

Cussac 2008 h2CVSV 9.49 ± 0.03 9.22 ± 0.02 8.52 ± 0.06

Lorcaserine Thomsen 2C? 6.95 ± 0.03 6.80 ± 0.08 6.76 ± 0.09 6.72 ± 0.01 7.82 ± 0.03 7.54 ± 0.12

Clozapine Banas, 2011, h2CINI, m2CVNi 7.97 ± 0.09

Knight 2004 h2CINI 7.60 ± 0.08 7.99 ± 0.09 7.87 ± 0.05

Shahid 2009 2C? 8.39 ± 0.03 8.79 ± 0.09 8.56 ± 0.06

Aripiprazole Banas, 2011, h2CINI, m2CVNi 7.21 ± 0.09

Schapiro 2003 h2CINI 8.06 ± 0.10 7.66 ± 0.08 9.44 ± 0.16 7.12 ± 0.09 7.12 ± 0.04

Shahid 2009 2C? 8.02 ± 0.16 9.59 ± 0.17 7.55 ± 0.14

RS1022221 Banas, 2011, h2CINI, m2CVNi 6.47 ± 0.02 6.52 ± 0.08 8.01 ± 0.30 7.72 ± 0.22

Knight 2004 h2CINI 5.54 ± 0.03 5.95 ± 0.06 8.30 ± 0.05

Cussac 2002 h2CVSV 6.63 ± 0.05 8.83 ± 0.04

SB215505 Banas, 2011, h2CINI, m2CVNi 8.12 ± 0.01 7.61 ± 0.21 7.40 ± 0.02 7.24 ± 0.26

Knight 2004 h2CINI

Cussac 2002 h2CVSV 8.83 ± 0.09 7.95 ± 0.06

SB206553 Banas, 2011, h2CINI, m2CVNi 8.29 ± 0.04 7.06 ± 0.41 8.24 ± 0.01 8.21 ± 0.24

Knight 2004 h2CINI 5.64 ± 0.09 7.65 ± 0.07 7.79 ± 0.07

Cussac 2002 h2CVSV 8.26 ± 0.17 8.50 ± 0.13

SB242084 Banas, 2011, h2CINI, m2CVNi 6.36 ± 0.02 6.07 ± 0.01 8.19 ± 0.22 5.93 ± 0.27

Knight 2004 h2CINI 6.07 ± 0.18 6.84 ± 0.28 8.15 ± 0.10

Cussac 2002 h2CVSV 7.34 ± 0.07 9.32 ± 0.06

Mesulergine Banas, 2011, h2CINI, m2CVNi 8.39 ± 0.2 7.81 ± 0.15 9.01 ± 0.01 8.53 ± 0.21

Knight 2004 h2CINI 7.34 ± 0.03 8.46 ± 0.05 8.74 ± 0.03

Cussac 2002 h2CVSV 8.71 ± 0.02 8.95 ± 0.06

RS127445 Banas, 2011, h2CINI, m2CVNi 8.51 ± 0.07 8.22 ± 0.24 5.63 ± 0.05 5.33 ± 0.45

Knight 2004 h2CINI 6.03 ± 0.13 8.97 ± 0.09 6.33 ± 0.10

MDL100907 Banas, 2011, h2CINI, m2CVNi 5.79 ± 0.60 5.03 ± 0.23 6.79 ± 0.51 6.64 ± 0.17

Knight 2004 h2CINI 8.73 ± 0.20 5.99 ± 0.06 7.52 ± 0.13

SB204741 Knight 2004 h2CINI b5.00 6.90 ± 0.27 5.56 ± 0.07

Cussac 2002 h2CVSV 7.29 ± 0.04 5.67 ± 0.11

Sarpogrelate Rashid 2003, 2C? 8.52 ± 0.12 6.57 ± 0.12 7.43 ± 0.03

Ketanserin Rashid 2003, 2C? 9.67 ± 0.12 6.55 ± 0.09 7.39 ± 0.11 L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36 17

has been reported for non-edited (and partially edited) 5-HT2C recep- 2.5. Oligomerization tors (Marion et al., 2004). This interaction leads to constitutive internalization (Marion et al., 2004), an effect prevented by inverse agonists Oligomeric associations of GPCRs often comprise signalling units,

(Chanrion et al., 2008). Calmodulin binds to the proximal region of the and 5-HT2A, 5-HT2B, and 5-HT2C receptors may all form homo- or het- 5-HT2C receptor C-terminus upon receptor activation by 5-HT. Mutation erodimers (Herrick-Davis et al., 2004; Brea et al., 2009; Jaffre et al., of this motif inhibits both β-arrestin recruitment to the 5-HT2C receptor 2009). In contrast to some classes of GPCRs, agonist binding does not and receptor-operated ERK1/2 signalling in HEK-293 cells, which is greatly influence the formation of 5-HT-receptor dimers, indicating independent of G proteins and dependent on β-arrestins. Expression a constitutive assembly before membrane insertion. For example, of the calmodulin mutant also prevents receptor-mediated ERK1/2 5-HT2C receptors generate dimers in the endoplasmic reticulum and phosphorylation in cultured cortical neurons and choroid plexus epithe- Golgi of living cells (Herrick-Davis et al., 2005). 5-HT2C receptor dimers lial cells that endogenously express 5-HT2C receptors (Labasque et al., possess an interface between transmembrane helices IV and V, and 2008). Intriguingly, although β-arrestins are implicated in the halluci- dimer proximity is increased and decreased by agonists and inverse nogenic effects mediated by 5-HT2A receptors, their trafficking is agonists, respectively (Mancia et al., 2008). Furthermore, analysis of independent (Bhatnagar et al., 2001). β-Arrestin 2 also directs agonist- functionally compensating, coexpressed mutant 5-HT2C receptors induced internalization of 5-HT2B receptors (Janoshazi et al., 2007). linked to Gq (fusion proteins) indicates that the dimer is asymmetric For instance, β-arrestins contribute to activation of ERK by the 5-HT2A, versus Gq, with both subunits binding to 5-HT and exerting distinct 5-HT2B, and 5-HT2C receptors. roles during signalling (Herrick-Davis et al., 2005; Mancia et al., 2008). PDZ (postsynaptic-density-95/disc-large/zonulla-occludens-1) The 5-HT2A and metabotropic glutamate 2 (mGlu2) receptors assem- domain-containing proteins profoundly influence the internalization ble into heterodimers via a transmembrane-IV and transmembrane-V of the 5-HT2A,2B,2C receptors, and PDZ proteins are essential for targeting linking domain (Gonzalez-Maeso et al., 2008). Intriguingly, mGlu2 5-HT2A receptors to dendrites in cortical neurons (Xia et al., 2003b). receptor agonists blunt heterodimer coupling to Gi, providing one sub- PDZ partners are both receptor- and function-specific. Thus, the specific strate for their anti-hallucinogenic properties (Gonzalez-Maeso et al., sets of PDZ proteins that interact with the 5-HT2A, 5-HT2B, or 5-HT2C 2008; Fribourg et al., 2011). Direct evidence of mGlu2/5-HT2A heterodi- receptors differ. Although PSD-95 (postsynaptic-density-95) prevents mers in the human brain and a reduced density of these heterodimers

5-HT2A receptor internalization (Xia et al., 2003a), it favours the consti- in patients with schizophrenia has been acquired (Gonzalez-Maeso tutive and agonist-dependent endocytosis of 5-HT2C receptors (Gavarini et al., 2008). Nonetheless, this study remains one of the few demonstra- et al., 2006). Conversely, MPP3 (membrane protein palmitoylated 3) sta- tions of heterodimers in tissues. Of particular interest are ligands specific bilizes 5-HT2C receptors at the plasma membrane (Gavarini et al., 2006). for 5-HT2A/mGlu2 complexes or other putative heterodimers possessing The 5-HT2B receptor shares the C-terminal E-X-V/I-S-X-V sequence with distinctive binding and coupling profiles (Gonzalez-Maeso et al., 2008). 5-HT2C receptors and also binds MUPP1-PDZ domains in vitro (Becamel Evidence of functional crosstalk between the 5-HT2A and D2 receptors et al., 2001). MUPP1 was shown to interact with the -SSV sequence was reported in HEK293 cells. D2 receptor activation increases the hallu- on the C-terminus of the 5-HT2C receptor. Moreover, 5-HT2A and cinogenic agonist affinity for the 5-HT2A receptor and decreases inositol 5-HT2B receptors sharing the C-terminal -E-X-V/I-S-X-V sequence with phosphate production. Co-immunoprecipitation studies show that 5-HT2C receptors also bind MUPP1-PDZ domains in vitro (Becamel these two receptors can physically interact in HEK293 cells and raise et al., 2001). The PDZ motif on the C-terminus of the 5-HT2B receptor the possibility that a receptor heterocomplex mediates the observed was also found to be necessary for the recruitment of the constitutive crosstalk. In vivo, 5-HT2A receptor expression is necessary for the full NO synthase (cNOS-NOS3)(Manivet et al., 2000). In addition, stimula- effects of a D2 antagonist on MK-801-induced locomotor activity tion of the 5-HT2B receptor triggered intracellular cGMP production (Albizu et al., 2011). Behavioural studies performed in mice lacking 5- through dual activation of NOS3 and inducible NOS (iNOS–NOS2). The HT2A receptors also revealed a remarkable 5-HT2A receptor-dependent group I PDZ motif at the carboxy terminus of the 5-HT2B receptor was dissociation in the beneficial antinociceptive effects of cannabinoid shown to be required for the recruitment of the NOS3 transduction CB1 receptors agonist delta-9-tetrahydrocannabinol (THC) and its detri- pathways, and NOS2 stimulation was controlled by the Gα13 pathways mental amnesic properties. Biochemical studies have shown that CB1

(Manivet et al., 2000). and 5-HT2A receptors form heteromers that are expressed and function- The human polyomavirus JCV causes the fatal demyelinating disease ally active in specific brain regions involved in memory impairment. progressive multifocal leukoencephalopathy in immunocompromised Remarkably, costimulation of both receptors by agonists reduces cell patients. Elphick et al. (2004) found that the 5-HT2A serotonergic recep- signalling; antagonist binding to one receptor blocks signalling of the tor could act as the cellular receptor on human glial cells for JCV. 5-HT2A interacting receptor; and heteromer formation leads to a switch in G pro- receptor antagonists inhibited JCV infection, and monoclonal antibodies tein coupling of the 5-HT2A receptor from Gq to Gi proteins (Vinals et al., targeting 5-HT2A receptors blocked the infection of glial cells by JCV but 2015). not by SV40. Transfection of 5-HT2A receptor-negative HeLa cells with a In cardiac fibroblasts, the angiotensin receptor AT1 and 5-HT2B re- 5-HT2A receptor restored virus infection, and this infection was blocked ceptors have been reported to share common signalling pathways, by an antibody targeting the 5-HT2A receptor. A tagged 5-HT2A receptor which support a possible direct interaction between 5-HT2B and colocalized with labelled JCV in an endosomal compartment following AT1 receptors. Using co-immunolocalization and a pull-down assay, internalization. Later, it was observed that endothelial cells not the two receptors were shown to interact together, which suggested expressing the 5-HT2A receptor could be infected. Following this that these receptors could exist in heterodimeric complexes (Jaffre et al., observation, it was reported that virus entry into HEK293A cells 2009), but in vivo experimental confirmation is still lacking. Ghrelin, was specifically observed when any of the 5-HT2 receptors were an orexigenic peptide present in the stomach, has gastroprokinetic expressed. Recent data confirmed that virus internalization into properties. In vivo studies have shown that the ghrelin receptor

HEK293A cells was signiﬁcantly and speciﬁcally allowed by 5-HT2A, (GHS-R1a) antagonist [D-Lys(3)]-GHRP-6 reduces food intake and 5-HT2B,or5-HT2C serotonin receptors in a way somewhat similar delays gastric emptying in rodents, but these effects are dissimilar to CCR5 chemokine receptor, which acts as a co-receptor for HIV-1 with the observed phenotype of ghrelin knockout mice. [D-Lys(3)]- viral entry. This work shows that the 5-HT2 subfamily of serotonin GHRP-6 induced a pronounced contraction of the stomach strips, receptors contributes to JCPyV infection by facilitating viral entry which was blocked by the 5-HT2 receptor antagonists methysergide (Assetta et al., 2013). and yohimbine resulting in smooth muscle contractions and suggesting

A better understanding of the interactions between viruses and the the possibility of direct interactions with 5-HT2B receptors (Depoortere 5-HT2 receptors may lead to new antiviral opportunities. et al., 2006). 18 L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36

A possibility for GHS-R1a/5-HT2C dimer-induced attenuation of a functional selectivity for specific intracellular signalling pathways calcium signalling was also observed. Flow cytometry fluorescence (Kenakin et al., 2012). 5-HT2 receptors couple to multiple intracellular resonance energy transfer (fcFRET) assays confirmed the direct interac- pathways including PLC and PLA2, and pharmacological evidence tion between the GHS-R1a receptor and 5-HT2C receptor. Colocalized using recombinant cell-based systems suggest that non-selective expression of the 5-HT2C and GHS-R1a receptors in cultured primary 5-HT2 agonists such as mCPP and quipazine may differentially activate hypothalamic and hippocampal rat neurons further supports the bio- these signalling pathways downstream from the 5-HT2C receptor logical relevance of this physiological interaction. When 5-HT2C recep- (Berg et al., 1998). Lysergic acid diethylamide and ergotamine displayed tor signalling is blocked, ghrelin's orexigenic effect is potentiated bias for β-arrestin signalling at 5-HT2B receptors; other ergolines such in vivo. In contrast, the 5-HT2C receptor-selective agonist lorcaserin as dihydroergotamine, methylergonovine, pergolide, and cabergoline attenuates ghrelin-induced food intake (Schellekens et al., 2015). also exerted similar effects. Ergotamine and dihydroergotamine, both

Physical associations of the melatonin MT2 and 5-HT2C receptors as of which contain a large tripeptide moiety substitution at the amide functional heteromers were also found by co-immunoprecipitation, scaffold, displayed more extreme signalling bias at the 5-HT2B receptor bioluminescence resonance energy transfer, and pharmacological tech- compared to lysergic acid diethylamide (Wacker et al., 2013). An addi- niques both in transfected cells and in cells from human cortex and hip- tional approach is the identiﬁcation of compounds with 5-HT2C receptor pocampus. MT2/5-HT2C heteromers amplify the 5-HT-mediated Gq/ agonist activity combined with antagonist activity at the 5-HT2A recep- phospholipase C response and trigger melatonin-induced unidirectional tor. Experimental evidence supports a potential synergy between these transactivation of the 5-HT2C protomer in MT2/5-HT2C heteromers. two pharmacological properties, raising the theoretical possibility that a Pharmacological studies reveal distinct functional properties for single drug possessing both characteristics may be a superior therapeu- agomelatine, which indicates “biased signalling” (Kamal et al., 2015). tic compared to either characteristic alone (Booth et al., 2009; Pockros Future studies must focus on the putative in situ heterodimerization et al., 2012; Cunningham et al., 2013; Canal et al., 2014). of native 5-HT receptors and on their pharmacological proﬁles with the Currently, it is unknown whether this example of functional selec- goal of identifying novel targets for therapeutic intervention. tivity could be translated into any therapeutic gain, although this notion does open up an interesting opportunity for future drug discovery. 2.6. Allosteric modulators

3. Pathologies and 5-HT2 receptors Positive allosteric modulators (PAMs) represent alternative approaches to orthosteric agonists (i.e., compounds that interact with 3.1. Fibrosis and inflammation the native ligand-binding site). PAMs can increase the affinity and/or efficacy of the orthosteric agonist for its target receptor by acting at a Healing is the process of the restoration of health in an unbalanced, site other than the native ligand-binding site (allostery). Importantly, diseased, or damaged organism. Fibrogenesis is a critical process in so-called pure GPCR PAMs, which lack intrinsic agonist activity within wound repair that generates scar tissue and helps protect an injured a specific signalling pathway, have been described. These compounds organ until the damaged or lost cells are regenerated. When an injury modulate the basal tone of the endogenous ligand in a manner that con- naturally resolves, the fibrogenic response is usually limited, and the serves the spatial and temporal elements of native neurotransmission temporary scar tissue replaced by healthy functional cells (Mann & (Christopoulos & Kenakin, 2002). Indeed, multiple PAMs have been Oakley, 2013). States of chronic tissue infection or damage, ageing, identified for GPCRs and may circumvent the challenges of orthosteric tumours, feeding habits and/or exposure to drugs that generate micro- agonists. First, PAMs could amplify endogenous signalling through the environments in which the inflammatory and fibrogenic phases of

5-HT2 receptors, likely resulting in a more physiologically relevant en- wound healing fail to resolve can induce a state of overactive wound hancement of function compared to a direct orthosteric agonist. Second, healing and loss of the normal regenerative process (Kapetanaki et al., because of generally higher sequence diversity in allosteric sites relative 2013; Mann & Oakley, 2013). This latter state can lead to the develop- to the conserved orthosteric domain, PAMs could potentially achieve ment of progressive ﬁbrotic disease, in which normal tissue is gradually higher receptor selectivity than orthosteric agonists. Indeed, some 5- replaced by scar tissue. This type of ﬁbrotic disease progression can

HT2C receptor PAMs have been reported, although the pharmacological occur as a consequence of uncontrolled repair processes in many organs profiles of these compounds have not yet been widely reported (Ding in response to a wide variety of chronic insults. Unless the underlying et al., 2012). Ergotamine has been shown to occupy two distinct sites injury process is effectively managed, the spread of fibrotic matrix in 5-HT2B receptors: the orthosteric site, where the indole nucleus of ultimately impairs the architecture and function of the organ. In fact, ergotamine resides, and an extended binding site, where the tripeptide fibrosis is the final common pathological outcome of many chronic portion is engaged. The allosteric site in the muscarinic M2 receptor and inflammatory diseases that subsequently leads to permanent is the same extracellular region as that interacting with the tripeptide scarring, organ malfunction, and ultimately death, as exemplified by portion of ergotamine. These similarities in both the M2 and 5-HT2B end-stage liver disease, chronic kidney disease, idiopathic pulmonary receptors suggest that the location of the extracellular allosteric site fibrosis, and heart failure. Fibrosis is also a major pathological feature for Class A GPCRs is quite similar and, in fact, argue that ergotamine of many chronic autoimmune diseases such as scleroderma, rheumatoid likely functions as a bitopic ligand; that is, ergotamine occupies both arthritis, Crohn's disease, ulcerative colitis, glomerulonephritis, and the orthosteric and putative extracellular allosteric site in the 5-HT2B myelofibrosis. Pathologic fibrosis can either affect a single organ or receptor. It is now thought that a sodium ion allosterically alters become systemic when it affects numerous organs, and its incidence the binding pocket to dampen G protein signalling, leaving β-arrestin increases with low exercise or a high-fat high sugar diet as well as recruitment intact. Recent structural considerations support that this with age and thus with the ageing of the population. However, the caus- sodium pocket is collapsed in the 5-HT2B receptor structure (McCorvy ative agents triggering the development of fibrosis are often unknown. &Roth,2015). The penetrance varies among gender; the female:male ratio is 3:1 for

The identification of specific PAMs of the 5-HT2 receptors may con- systemic sclerosis and lung fibrosis and nearly the opposite for kidney, ceivably lead to improved therapeutics. liver, and heart fibrosis. Over the last decade, several investigations revealed the fact that the 2.7. Biased agonists 5-HT system is activated during the early phases of wound repair and exerts a major influence on fibrogenesis. Modulating the activities of

Another area for the development of agonists targeting 5-HT2 recep- speciﬁc 5-HT receptors that trigger the activation of ﬁbrogenic signal tors might emerge from so-called biased agonist compounds that share transduction seems to be a promising approach to control pathological L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36 19

fibrosis. Mechanistic links between fibrosis and 5-HT were first reported and ameliorates established fibrosis by decreasing the mRNA levels in the 1960s for a condition known as carcinoid syndrome, which is of TGF-β1, connective tissue growth factor, plasminogen activator caused by tumours arising from neuroendocrine enterochromaffin inhibitor-1 and Smad-3 (Dees et al., 2011). Moreover, inhibition of cells that synthesize 5-HT in the gut (i.e., carcinoid tumours that secrete platelet activation prevents fibrosis in different rodent models (including vast quantities of 5-HT). While there is still much to learn about the bleomycin-induced) of skin fibrosis. Consistently, mice deficient for method by which 5-HT and its different receptors converge in various TPH1, which is the rate-limiting enzyme for 5-HT production outside target cell types to regulate tissue fibrotic repair, initial evidence the central nervous system, show reduced experimental skin fibrosis reported the implication of the 5-HT2 receptor subtypes in different (Dees et al., 2011). pathological fibrotic tissues, including skin (Dees et al., 2011), lung (Launay et al., 2002), heart (Jaffre et al., 2009; Pavone et al., 2012), 3.1.4. Heart fibrosis valves (Ayme-Dietrich et al., 2012), and liver (Ebrahimkhani et al., In rats, treatment of neonatal cardiac fibroblasts with 5-HT increases 2011). In addition to fibroblasts, these same receptors have been the expression of smooth muscle α-actin (a marker of fibroblast differ- identified in haematopoietic stem cells (Amireault et al., 2011; entiation into myofibroblasts), stimulates their migration, and enhances Launay et al., 2012)andimmunecells(de Las Casas-Engel et al., the secretion of TGF-β1 and expression of MMPs, all of which seem to be

2013), which also contribute to fibrosis. mediated through 5-HT2A receptors (Yabanoglu et al., 2009). Indepen- However, there is still a complete lack of therapeutic compounds dently, either 5-HT- or AngII-stimulated cytokine release, including that target a specific 5-HT receptor and are selective for treating fibrotic the secretion of IL-6, IL-1β, TNF-α, and TGF-β1 in adult cardiac fibro- diseases. blasts is sensitive to 5-HT2B receptor blockade. Treatments with epider- mal growth factor receptor (EGFR, ErbB1/4)-selective inhibitors or 3.1.1. Lung fibrosis selective inhibitors of MMPs also abolish AngII- and 5-HT-induced cyto- In mouse lung homogenates, 5-HT concentrations significantly kine release. Finally, the use of HB-EGF−/− cardiac fibroblasts confirms increase over the progression of bleomycin-induced fibrosis, with max- that EGFR transactivation is absolutely required for AngII- and 5-HT- imum values observed at day seven; these increases occur in conjunc- dependent cytokine release. Collectively, these results reveal that the tion with increased expression of the 5-HT2A and 5-HT2B receptors convergent actions of AngII and 5-HT via interactions between the (Königshoff et al., 2010). Pharmacological blockade of either the AT1 and 5-HT2B receptors coexpressed in non-cardiomyocytes are the 5-HT2A or 5-HT2B receptors reduces bleomycin-induced lung fibrosis, key limiting events in cardiac fibroblast activation (Jaffre et al., 2009). as demonstrated by reduced lung collagen content and reduced Embryonic morphogenesis of cardiac valves and fibrotic events is a procollagen 1 and procollagen 3 mRNA expression levels. Serotonin critical event linked to endothelial-mesenchymal transformation antagonists promote an antifibrotic environment by decreasing the (EMT). Inducers of EMT during valvulogenesis include VEGF, TGF-β1, lung mRNA levels of TGF-β1, connective tissue growth factor and plas- and Wnt/β-catenin, all of which are regulated in a spatiotemporal minogen activator inhibitor-1 as well as JunD mRNA. Interestingly, the manner. Serotonin can initiate TGF-β signalling, which in turn has

5-HT2B receptor is strongly overexpressed in fibroblasts originating been strongly implicated in fibrosis. Recent evidence has suggested from the fibroblastic foci in either human idiopathic pulmonary fibrosis that degenerative valvular disease may be mediated by developmental samples or bleomycin-induced pulmonary fibrosis samples in rodents pathways including bone morphogenic protein (BMP), Wnt and Notch (Fabre et al., 2008). signalling, nitric oxide, and angiotensin II (Orton et al., 2012). Wnt2 acts as an angiogenic factor for endothelium in vitro and in vivo, and 3.1.2. Liver fibrosis its target genes undergo complex regulation by the tissue microenvi-

In the liver, fibrogenic hepatic stellate cells (HSC), which are nega- ronment (Klein et al., 2009). Gene profiling identified 5-HT2B as a down- tive regulators of hepatocyte regeneration, are known to express regulated target gene of Wnt2 signalling in HUVECs. The existence

5-HT2A and 5-HT2B receptors that regulate TGF-β1 and the downstream of valve interstitial cells derived at different times and from different signalling Smads (Li et al., 2006). HSCs are key cellular components origins (i.e., the embryonic epicardium and endocardial cushions and of hepatic wound healing and fibrosis. After HSC activation, expression adult bone marrow) raises the interesting possibility that these popula- of 5-HT2A and 5-HT2B receptors becomes 100- and 50-fold that of quies- tions of fibroblasts are functionally different and thus differ in their cent cells, respectively. Treatment of HSCs with 5-HT2 receptor antago- susceptibility to and/or participation in fibrotic pathological processes nists suppresses proliferation and increases their rate of apoptosis. (Visconti et al., 2006).

Serotonin synergizes with platelet-derived growth factor to stimulate If correct, deciphering the contribution of 5-HT2 receptors in these increased HSC proliferation (Ruddell et al., 2006). Distinct from quies- events should advance our understanding of fibrosis and lead to new cent cells, activated HSCs exhibit transient [Ca2+]i increases following antifibrotic compounds. treatment with 5-HT that are blocked by 5-HT2 receptor antagonists (Park et al., 2011). Stimulation of 5-HT2B receptors on HSCs by 5-HT 3.2. Central nervous system was recently shown to activate the expression of TGF-β1 (a powerful (depression, psychosis, addiction, feeding, impulsivity) suppressor of hepatocyte proliferation) via ERK/JunD signalling. Selec- tive antagonism of 5-HT2B receptors enhanced hepatocyte growth in 3.2.1. Feeding and anorexigens models of acute and chronic liver injury. Similar effects are observed Maintenance of energy balance requires regulation of the amount in mice lacking either 5-HT2B or JunD as well as when HSCs are selec- and timing of food intake. Eating disorders are an important health tively depleted. Antagonism of 5-HT2B attenuates CCL4-induced liver problem in developed countries (Leibowitz & Alexander, 1998; fibrogenesis and improves liver function in disease models in which Vickers & Dourish, 2004); see (http://www.cdc.gov/obesity/data/facts. fibrosis is pre-established and progressive (Ebrahimkhani et al., 2011). html). It has been well established that in the central nervous system, 5-HT is one of the major neurotransmitters that control numerous 3.1.3. Skin fibrosis physiological processes affecting food intake. The most extensive

In skin experiencing systemic sclerosis (SSc), expression of 5-HT2B characterization of the serotonergic influences on energy balance path- receptors was strongly increased in the fibrotic tissue of patients, ways relates to the modulation of the arcuate nucleus POMCs and NPY/ and almost all fibroblasts stained positive for 5-HT2B receptors. Der- AgRP neuronal populations. Previous studies have established that −/− mal fibrosis is reduced in Htr2B mice using both inducible and released 5-HT (i) hyperpolarizes and inhibits AgRP/NPY neurons and genetic models of fibrosis. Pharmacologic inactivation of the 5-HT2B decreases the inhibitory drive onto POMC cells by activation of 5-HT1B receptor also effectively prevents the onset of experimental fibrosis receptors and (ii) activates POMC/CART neurons via stimulation of 20 L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36

5-HT2C receptors (Heisler et al., 2006), which leads to reciprocal in- phosphorylation of SERT (Launay et al., 2006) may explain the require- creases in α-MSH release and decreases in AgRP release at melanocortin ment of 5-HT2B receptors in the release action. These findings strongly 4 receptors in the target regions. Subsequent increases in 5-HT neuro- support that activation of 5-HT2B receptors is a limiting step in the transmission have also been shown to regulate the hypothalamic– SERT-dependent release effect of DF, whereas other 5-HT receptors pituitary–adrenal (HPA) axis upstream of corticotropin-releasing hor- may act downstream with respect to feeding behaviour. The results mone among others (Heisler et al., 2007). Many studies have suggested using the 5-HT2C receptor agonist WAY-161503 (Rosenzweig-Lipson −/− that 5-HT1B receptor activation inhibits neurons that promote hunger, et al., 2006)inHtr2B mice confirm the participation of 5-HT2C recep- while 5-HT2C receptors activate neurons in the hypothalamic nuclei tors in feeding behaviour (Banas et al., 2011) as observed in humans that promote satiety (Heisler et al., 2006; Nonogaki et al., 2007; Lam during the recent clinical trial for the 5-HT2C receptor-selective agonist et al., 2008). However, activation of these receptors is not sufficient to lorcaserin (Smith et al., 2010; Thomsen et al., 2008). Moreover, it has fully explain the modulatory effects of 5-HT in feeding behaviour. been reported that 5-HT2C receptor-expressing POMC neurons are Other 5-HT receptors such as 5-HT4 or 5-HT6 have also been suggested required to control energy and glucose homeostasis (Berglund et al., to participate in the control of energy intake (Vickers & Dourish, 2004; 2013). Nevertheless, postsynaptic receptors including the 5-HT1B, Conductier et al., 2005; Jean et al., 2007). 5-HT2C, and possibly 5-HT2B receptors seem to be indirectly activated Dexfenfluramine (d-fenfluramine, DF) is an amphetamine congener by DF-induced SERT-dependent and 5-HT2B receptor-dependent 5-HT that has been utilized therapeutically as a highly efficient anorectic mol- release. Central 5-HT neurons have recently been reported to play a ecule for the treatment of obesity (Garfield & Heisler, 2009). Previously, major role in regulating glucose and lipid homeostasis through the re- DF was used in the treatment of obesity and had potential for the treat- cruitment and metabolic activation of brown and beige adipocytes ment of bulimia. However, clinical use of DF has been associated with (McGlashon et al., 2015). several unacceptable side effects including primary pulmonary hyper- The interplay between the central and peripheral 5-HT regulation of tension and valvular heart disease (Fitzgerald et al., 2000; Rothman feeding behaviour and energy homeostasis has not yet been elucidated. et al., 2000; Launay et al., 2002), and this anorexigen was withdrawn from the market in 1997. In the early 1980s, Mennini and colleagues performed pioneering work initially describing the effect of DF and 3.2.2. Raphe neurons and depression derivatives on the release of 5-HT into nerve terminals by targeting In the raphe nuclei, neurotransmission by 5-HT is tightly regulated by the serotonin transporter (SERT) (Garattini et al., 1986). Administration autoreceptors that fine-tune serotonergic neurotransmission through of DF suppresses food intake in both animals and humans. Animal stud- negative feedback inhibition at either the cell bodies (predominantly ies have reported either a complete or partial blockade of DF-induced 5-HT1A) or the axon terminals (predominantly 5-HT1B); however, dif- hypophagia by the 5-HT2 antagonist ritanserin (Goodall et al., 1993; ferent roles for 5-HT2B receptors have also been identified (McDevitt Neill & Cooper, 1989), the 5-HT2B/2C antagonist SB-200646 (Bourson & Neumaier, 2011). The therapeutic effects induced by serotonin- et al., 1996) and the 5-HT2C antagonist SB242084 (Clifton et al., 2000). selective reuptake inhibitor (SSRI) antidepressants are initially triggered Thus, the anorectic effect of DF has been proposed to be mediated by by blocking the SERT and rely on long-term adaptations of pre- and post- activation of 5-HT2C receptors (Vickers et al., 1999, 2001), while synaptic receptors. 5-HT2B receptors have been shown to participate in the DF-induced pul- The 5-HT2 receptor agonist DOI decreases the firing rate of 5-HT monary hypertension (Launay et al., 2002) and valvulopathy (Setola neurons in the dorsal raphe (DR) nucleus of anaesthetised WT mice. −/− et al., 2005). Since the hypophagic effect of DF persisted in 5-HT2C recep- This inhibitory response persists in Htr2C mice but is completely −/− −/− tor knockout (Htr2C )mice(Vickers et al., 1999), other 5-HT receptor blunted in Htr2A knockout mice. Moreover, the reduction of DR 5-HT subtypes must be involved in DF-induced hypophagia. neuronal activity in WT mice by DOI can be attenuated by the loss

The 5-HT2B receptor has also been proposed to play a role in the of norepinephrine (NE) neurons. In WT mice, pharmacological inactiva- regulation of food intake (De Vry & Schreiber, 2000). An early study tion of 5-HT2A receptors by the selective antagonist MDL100907 showed an orexigenic effect of the preferential 5-HT2B receptor agonist reverses the escitalopram-induced decrease in DR 5-HT neuronal activ- BW723C86 (Kennett et al., 1997). Furthermore, it has been reported ity. In microdialysis experiments, a single injection of escitalopram that 5-HT regulates appetite possibly via 5-HT2B receptors expressed increases cortical extracellular 5-HT but not NE levels in awake WT on hypothalamic neurons (Yadav et al., 2009). In particular, POMC- mice. Although the addition of MDL100907 does not potentiate 5-HT −/− speciﬁc Htr2B mice show mild hypophagia and a reduction in fat pad neurotransmission, it allows escitalopram to increase cortical NE out- mass. Like all 5-HT2 receptors, the 5-HT2B receptor is Gq-coupled and ﬂow and consequently elicit an increase in swim time in the forced therefore excitatory, while POMC neurons have a well-established an- swimming test. Blockade of the 5-HT2A receptor may strengthen the orexigenic function. The mechanisms through which 5-HT2B receptors antidepressant-like effect of escitalopram by facilitating the enhance- on POMC neurons may produce orexigenic effects have not been ment of NE transmission in the brain (Quesseveur et al., 2013). established. Reports that 5-HT2B receptors on POMC neurons mediate These results provide support for the use of atypical antipsychotics orexigenic effects are especially puzzling since a series of studies recently (which target 5-HT2 receptors), with SSRIs as a relevant antidepressant reported that expression of the 5-HT2C receptor on POMC neurons has a augmentation strategy. critical anorexigenic function (Xu et al., 2008). Both short-term and long-term behavioural and neurogenic SSRI Whether and how multiple types of 5-HT receptors might be effects were abolished after either genetic or pharmacologic inactiva- functioning with overlapping purposes in the same or different population of 5-HT2B receptors (Diaz et al., 2012). Conversely, direct agonist tions of POMC neurons are open questions that require additional stimulation by the preferential 5-HT2B receptor agonist BW723C86 investigation. induced an SSRI-like response in acute behavioural and chronic neuro-

Interestingly, the hypophagic response to the anorexigen and 5-HT genic assays. The 5-HT2B receptor is expressed in raphe serotonergic releaser DF as observed in wild-type (WT) mice was eliminated in neurons as shown by single cell PCR. The SSRI-induced increase in the −/− Htr2B mice and in WT mice treated with the highly selective 5-HT2B hippocampal extracellular 5-HT concentration was strongly reduced in receptor antagonist RS127445. Using microdialysis, the DF-induced the absence of functional 5-HT2B receptors. These results support the hypothalamic peak of 5-HT release was found to be strongly reduced positive regulation of serotonergic neurons by 5-HT2B receptors (Diaz −/− in conscious Htr2B mice compared with WT mice. Moreover, the pro- et al., 2012). nounced 5-HT release observed upon DF stimulation of a synaptosomal Based on this observation, the 5-HT2B receptor appears to positively preparation from WT mice was not observed in the synaptosomes modulate serotonergic activity and to be required for the therapeutic −/− from Htr2B mice (Banas et al., 2011). 5-HT2B receptor-dependent actions of SSRIs, although direct 5-HT2B agonists cannot be used as L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36 21 therapeutic option unless a biased agonist without the adverse cardio- nucleus accumbens (NAcc) and of 5-HT and NE in the prefrontal cortex. −/− pulmonary effects could be developed. Self-administration of MDMA is blunted in Htr2A mice compared to Evidence from various sources indicates alterations in the function of their WT littermates. Horizontal locomotion is increased by MDMA ad- −/− the 5-HT2C receptor with regard to anxiety, depression, suicide, and ministration to a higher extent in Htr2A than in WT mice. DA outﬂow in −/− other stress-related disorders upon treatment with antidepressant the NAcc is lower in Htr2A compared to WT mice under basal condi- drugs. Although the notion of 5-HT2C receptor desensitization following tions and after MDMA challenge. In WT mice, priming does not reinstate antidepressant treatment is well established in the literature, this MDMA-seeking behaviour, while cue-induced reinstatement is promi- concept is mainly based on in vitro assays and/or behavioural assays nent. This cue-induced reinstatement is blocked by the administration

(hypolocomotion, hyperthermia) that have poor relevance to anxio- of the 5-HT2A receptor-selective antagonist SR46349B (eplivanserin). depressive disorders. Various serotonergic projections to distinct 5-HT2A receptors are crucial for MDMA-induced reinforcement and 5-HT2C receptor populations exert complex modulations. Targeting cue-induced reinstatement of MDMA-seeking behaviour. These effects the 5-HT2C receptor in specific brain areas rather than activating or are probably due to the modulation of mesolimbic dopaminergic blocking the receptors in the whole brain would be the most rational activity (Orejarena et al., 2011). An increase in the functionality of cor- therapeutic strategy (Martin et al., 2014). Nevertheless, agomelatine, tical 5-HT2A receptors was observed in mice pretreated with MDMA which is a potent melatonin receptor agonist, is also an effective antide- compared with mice pretreated with saline, but this activation was pressant and a potent 5-HT2B/2C receptor antagonist (Millan et al., significantly greater in pretreated mice in the locomotor environ- 2003). Administration of melatonin twice daily increases the number ment. In contrast, the functional activity of striatal D2 receptors of spontaneously active dopamine (DA) neurons but does not affect was significantly decreased only in mice pretreated with MDMA. the firing of NE neurons. Long-term administration of either melatonin These results reveal neuroadaptations in cortical 5-HT2A and striatal or the 5-HT2C receptor antagonist SB242084 alone has no effect on the D2 receptors after MDMA-induced behavioural sensitization in mice firing rate and burst parameters of dorsal raphe 5-HT and ventral teg- (Varela et al., 2011). Using in vivo microdialysis and locomotor mental area DA neurons. The combination of both drugs, however, activity monitoring, repeated injections of MDMA induce long-term only enhances the number of spontaneously active DA neurons while sensitization of noradrenergic and serotonergic neurons, which cor- leaving the firing rate of 5-HT neurons unchanged. The addition of the relates with behavioural sensitization. The development of this phe- selective 5-HT2B receptor antagonist LY266097, which by itself is devoid nomenon, which lasts for at least 1 month after withdrawal, requires of any effect, to this combinatory regimen increases the number of repeated stimulation of the α1B-adrenergic and 5-HT2A receptors. bursts per minute and the percentage of spikes occurring in bursts of Moreover, behavioural and neuroendocrine assays indicate that DA neurons (Chenu et al., 2014). In conclusion, the combination of mel- hyper-reactivity of noradrenergic and serotonergic networks is asso- atonin receptor activation and 5-HT2C receptor blockade results in a dis- ciated with persistent desensitization of the somatodendritic α2A- inhibition of DA neurons; when 5-HT2B receptors are also blocked, the adrenergic, 5-HT2A,and5-HT1A receptors. Repeated MDMA exposure firing and the bursting activity of DA neurons are both enhanced, thus causes strong neural and behavioural adaptations, and inhibitory reproducing the antidepressant effect of agomelatine and supporting feedback mediated by α2A-adrenergic and 5-HT1A autoreceptors the effect of these receptors on DA neurons. plays an important role in the physiopathology of this addictive behaviour (Lanteri et al., 2014).

3.2.3. Drugs of abuse The central 5-HT2B receptor has been only recently considered as Dopaminergic projections to the striatum inhibit the medium spiny an interesting pharmacological target to treat drug addiction. Acute neurons (MSN) in the striatopallidal (indirect) pathway and excite pharmacological inhibition or genetic ablation of the 5-HT2B receptor MSNs in the striatonigral (direct) pathway. There are dense 5-HT pro- in mice completely abolishes MDMA-induced hyperlocomotion and jections to the striatum from the dorsal raphe nucleus, and it is known 5-HT release in the NAcc and ventral tegmental area. Furthermore, the that increased 5-HT in the striatum facilitates DA release from terminals. 5-HT2B receptor dependence of MDMA-stimulated release of endoge- The direct pathway excites various cortical nuclei, and some of these nous 5-HT from superfused midbrain synaptosomes suggests that nuclei send inhibitory projections to the DRN (dorsal raphe nuclei). 5-HT2B receptors act to favour MDMA-stimulated 5-HT release. Thus, Among drugs of abuse, cocaine blocks all 3 monoamine transporters the 5-HT2B receptor is a regulatory component in the actions of −/− at similar concentrations, amphetamine and methamphetamine are MDMA (Doly et al., 2008). Htr2B mice did not exhibit behavioural most potent at the norepinephrine transporter (NET) but 5- to 9-fold sensitization or conditioned place preference following MDMA injec- less potent at the dopamine transporter (DAT) and 200- to 500-fold less tions. In addition, both MDMA-induced reinstatement of conditioned potent at SERT; the compound 3,4-methylenedioxymethamphetamine place preference after extinction and locomotor sensitization develop- (MDMA or ‘ecstasy’) has a higher afﬁnity for SERT than either DAT or ment are abolished by treatment with RS127445 in WT mice. Accordingly, NET (Han & Gu, 2006). MDMA-induced dopamine D1 receptor-dependent phosphorylation of extracellular regulated kinase in the NAcc is abolished in mice lacking

3.2.3.1. MDMA and its metabolite MDA. The amphetamine derivative functional 5-HT2B receptors. These results underpin the importance of MDMA is a psychostimulant drug that is widely used recreationally 5-HT2B receptors in the reinforcing properties of MDMA (Doly et al., among young people in Europe and North America. MDMA is metabo- 2009). lized into N-demethylated metabolite 3,4-methylenedioxyamphetamine The selective 5-HT2C receptor antagonist RS102221 can suppress (MDA). The serotonergic system appears crucial for the reinforcing prop- MDMA-induced hyperlocomotion. These ﬁndings provide evidence erties of MDMA. MDMA binds preferentially to and reverses the activity that inactivation of 5-HT2C receptors may reduce the motor response of the SERT, which also causes a release of 5-HT stores from nerve termi- to MDMA (Conductier et al., 2005). A role has been ascribed to the nals. Subsequent activation of postsynaptic 5-HT receptors by released inhibitory effects of 5-HT2C receptor activation on the physiology and 5-HT has been shown to be critical for the unique psychostimulatory behaviour mediated by the mesolimbic dopaminergic pathway, particu- effects of MDMA. larly in the terminal region of the NAcc. The inﬂuence of this receptor

Current evidence indicates that 5-HT2A receptors modulate subtype on functions mediated by the nigrostriatal dopaminergic path- mesolimbic DA activity and several behavioural responses related way is less clear. to the addictive properties of psychostimulants. A study evaluating Therefore, the contribution of 5-HT2 receptors to the psycho- the role of 5-HT2A receptors in MDMA-induced reinforcement, hyper- stimulant effects of MDMA is complex, with the 5-HT2A and 5-HT2B locomotion, and the reinstatement of MDMA-seeking behaviour inves- receptors responsible for enhanced effects but the 5-HT2C receptor tigated the basal and MDMA-stimulated extracellular levels of DA in the lowering the effects of MDMA. 22 L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36

3.2.3.2. Amphetamine. Although the locomotor response to d- The peripheral administration of the selective 5-HT2B receptor amphetamine is mediated by an increased release of DA and NE, block- antagonists RS127445 or LY266097 significantly reduced basal DA out- ade of either the α1B-adrenergic or 5-HT2A receptors almost completely flow in the NAcc shell but had no effect on cocaine-induced DA outflow inhibits the d-amphetamine-induced locomotor response in mice. In in this brain region. Additionally, RS127445 failed to modify both basal agreement with these results, mice lacking α1B-adrenergic receptors and cocaine-induced DA outflow in the NAcc core and the DSt. This hardly respond to d-amphetamine. Paradoxically, mice lacking 5-HT2A interaction may occur downstream of DA neurons and could involve −/− receptors (Htr2A ) exhibit a twofold higher locomotor response to activity at the level of DSt and/or NAcc DA transmission in keeping d-amphetamine than their WT littermates. Repeated amphetamine with the importance of these brain regions in the behavioural responses −/− injections still increase the locomotor response of Htr2A mice to to cocaine. Regulatory control may therefore be exerted by the 5-HT2B d-amphetamine at a level similar to that of sensitized WT mice. A receptor on ascending DA pathways (Devroye et al., 2015).

1 mg/kg dose of prazosin, an α1B-adrenergic antagonist, completely Thus, 5-HT2B receptors may also exert facilitatory control on −/− blocks d-amphetamine-induced locomotor response in Htr2A naïve mesoaccumbens DA pathway activity in addition to serotonergic −/− animals, but a dose of 3 mg/kg is necessary in sensitized Htr2A mice. neurons. −/− −/− Because naïve Htr2A mice exhibit an increased cortical noradrenergic Htr2C mice completely devoid of 5-HT2C receptors display en- response to d-amphetamine, these data confirmed that repeated hanced exploration of a novel environment and increased sensitivity −/− d-amphetamine modifies noradrenergic transmission in Htr2A mice. to the stimulatory locomotor effects of cocaine. In an operant intrave- Stimulation of 5-HT2A receptors would inhibit noradrenergic neurons. nous self-administration model under a progressive ratio schedule of −/− The dramatic decrease in 5-HT2A receptor antagonist efficiency in sensi- reinforcement, Htr2C mice display elevated numbers of lever pressing tized WT mice indicates that disruption of the regulatory role of 5-HT2A for cocaine injections, indicating that the drug is more reinforcing in −/− receptors on noradrenergic transmission occurs during sensitization these mice. Moreover, Htr2C mice exhibit enhanced cocaine-induced and thus represents a putative physiological basis of the behavioural elevations of DA levels in the NAcc, a brain region implicated in the sensitization to d-amphetamine (Salomon et al., 2007). stimulant and rewarding properties of cocaine. In contrast, phenotypic

Acute exposure to the selective 5-HT2B receptor antagonist differences in DSt DA levels were not observed after cocaine treatment. LY266097 significantly diminished the increase in DA outflow induced These findings strongly implicate 5-HT2C receptors in the serotonergic by d-amphetamine in the ventral striatum/NAcc but not in the dorsal suppression of DA-mediated behavioural responses to cocaine (Rocha −/− striatum (DSt) (Auclair et al., 2010). The locomotor response of Htr2B et al., 2002). Depleting forebrain 5-HT levels induces compulsive mice to d-amphetamine was found to be significantly enhanced com- cocaine-seeking behaviour in rats with a limited history of cocaine +/+ pared with Htr2B mice (Pitychoutis et al., 2015), supporting the notion use; this can be reversed by systemic treatment with a 5-HT2C receptor −/− of this receptor participating in the control of DA/NE pathways. Htr2C agonist and mimicked by systemic treatment with a 5-HT2C receptor mice showed marked alterations in the activity and functional output antagonist in intact animals (Pelloux et al., 2012). −/− of the DA pathway. Htr2C mice also displayed increased activity These results indicate the causal involvement of reduced serotonin- of substantia nigra pars compacta (SNc) DA neurons, elevated baseline ergic transmission in the emergence of compulsive drug seeking after a extracellular DA concentrations in the DSt, alterations in grooming long history of cocaine use that is dependent on 5-HT2C receptors. behaviour, and enhanced sensitivity to the stereotypic behavioural effects of d-amphetamine and the DAT blocker GBR 12909. These psychostimulant responses occurred in the absence of phenotypic dif- 3.2.4. Impulsivity ferences in the drug-induced extracellular DA concentration, suggesting A feature of multiple neuropsychiatric disorders is impulsivity. Re- a phenotypic alteration in behavioural responses to released DA. This cent studies have implicated 5-HT systems (notably the 5-HT2 receptor) possibility was further suggested by enhanced behavioural responses in the medial prefrontal cortex (mPFC) in mediating individual differ- −/− of Htr2C mice to the D1 receptor agonist SKF 81297; similar responses ences in motor impulsivity. High and low impulsive rats were identified −/− were also observed in Htr2B mice (Bevilacqua et al., 2010). Differences in a 1-choice serial reaction time task (1-CSRTT). In western blots, in DSt D1 or D2 receptor expression were not found, nor were there any protein levels of the 5-HT2A and 5-HT2C receptors predicted the intensity differences in the medium spiny neuron firing patterns or intrinsic of motor impulsivity, and their ratio in the mPFC was positively corre- membrane properties following DA stimulation (Abdallah et al., 2009). lated with levels of premature responses in individual outbred rats.

Therefore, 5-HT2B/2C receptors regulate nigrostriatal dopaminergic High phenotypic motor impulsivity is associated with diminished activity and function both on SNc dopaminergic neurons and on a co-immunoprecipitation of mPFC synaptosomal 5-HT2A and 5-HT2C locus downstream of the DSt, whereas 5-HT2A receptors act on NE receptors. The shRNA knockdown of the 5-HT2C receptor in the mPFC re- neurons. sults in increased motor impulsivity and triggers a functional disruption

of the local 5-HT2A:5-HT2C receptor ratio as evidenced by a compensatory upregulation of 5-HT2A receptor protein expression and a leftward shift in 3.2.3.3. Cocaine. Several studies indicate that acute treatment with the potency of M100907 to suppress impulsive behaviour. There seems

5-HT2A receptor antagonists attenuates the reinstatement of cocaine- to be a direct relationship between the 5-HT2A and 5-HT2C receptors in maintained behaviour but not cocaine self-administration in rodents. the mPFC, and their imbalance may be a functionally relevant mechanism

Investigation of the effects of the selective 5-HT2A receptor antagonist in motor impulsivity (Anastasio et al., 2015). MDL100907 on intravenous cocaine self-administration as well as A functional polymorphism in the human HTR2B gene that intro- drug and cue-primed reinstatement was performed in rhesus macaques. duces a stop codon after 20 amino acids (Q20*) was found to enhance

The role of 5-HT2A receptors in cocaine-induced DA overflow in the NAcc impulsive behaviour (Bevilacqua et al., 2010). Especially under condi- and the caudate nucleus/DSt was evaluated using in vivo microdialysis. tions where control was impaired, the carriers of this stop codon were MDL100907 significantly attenuates drug- and cue-induced reinstate- more vulnerable to alcohol and were more impulsive if they drank. −/− ment but had no significant effects on cocaine self-administration across Similarly, Htr2B mice displayed more impulsive choices in delayed a range of maintenance doses. Importantly, MDL100907 attenuates discounting tasks, sought novelty and were more active after receiving cocaine-induced DA overflow in the DSt but not in the NAcc (Murnane a D1 dopamine receptor agonist (Bevilacqua et al., 2010). The pheno- −/− et al., 2013). type of Htr2B mice results from a combination of both the direct This work revealed that 5-HT2A receptors differentially contribute to absence of 5-HT2B receptor signalling and the neural adaptations trig- the abuse-related effects of cocaine and cocaine-induced nigrostriatal gered by the permanent lack of signalling through this receptor during and mesolimbic DA overflow. development. L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36 23

−/− In operant-based behavioural paradigms, Htr2C mice display defi- thalamus of 5-HT2A receptor-deficient mice rescued the otherwise −/− cits in executive functions. Htr2C mice are impaired in the acquisition absent potentiation of NMDA transmission, induction of temporal plas- of a visuospatial attention task as assessed in the 5-CSRTT. In this task, ticity, and deficit in associative memory (Barre et al., 2016). −/− Htr2C mice exhibit marked impairment of attentional processes with In a Finnish cohort of impulsive patients (Bevilacqua et al., 2010), normal response inhibition. Based on the results from in vivo microdial- early onset schizophrenia was more prevalent in HTR2B Q*20 carriers. −/− ysis, the elevated extracellular DA concentrations in the NAcc of Htr2C Recently, it was shown that domains related to the positive, negative, mice during task performance indicate that 5-HT2C receptors impact DA and cognitive symptom clusters of schizophrenia are affected in −/− homeostasis during a visuospatial attention task. The disinhibition of Htr2B mice as shown by deficits in sensorimotor gating, selective mesolimbic DA pathways may contribute to the impaired attention attention, social interactions, and processes involving learning and −/− −/− and perturbed task performance in Htr2C mice. Additionally, in a spa- memory. In addition, Htr2B mice present with an enhanced locomotor −/− tial reversal-learning task, Htr2C mice failed to improve their perfor- response to the NMDA receptor antagonist dizocilpine and the mance over a series of reversals, indicating that intact 5-HT2C receptor psychostimulant amphetamine, with robust alterations in sleep archi- signalling is required to accurately respond to repeated changes in tecture. Importantly, selected schizophrenic-like phenotypes and −/− reward contingencies. In contrast to the Htr2C mice phenotype in the endophenotypes are rescued by chronic haloperidol treatment 5-CSRTT, WT mice treated with the 5-HT2C receptor antagonist (Pitychoutis et al., 2015). Owing to its relatively low expression level SB242084 exhibited a diminished response inhibition, suggesting differ- in the brain, the 5-HT2B receptor has not received much of the limelight ent effects between acute pharmacological blockade and constitutive as a possible regulator of the DOI-induced HTR. The effects of DOI on loss of 5-HT2C receptor activity (Pennanen et al., 2013). These findings HTR induction are increased in 5-HT2B receptor knockout mice (Luc suggest that impaired 5-HT2C receptor signalling during development Maroteaux, unpublished). Interestingly, although the ergoline analogue may predispose the organism to executive function disorders. lisuride has 5-HT2A receptor agonist activity, it does not produce the HTR and is a potent antagonist of 5-HT2B receptors. It is worth consider- 3.2.5. Psychosis ing the 5-HT2B receptor as a potential modulator of the behavioural The head-twitch behavioural response (HTR-rapid lateral move- effects of DOI. For example, 5-HT2B receptor affinity of hallucinogenic ments of the head) in rodents is reliably elicited by a variety of psyche- phenylisopropalamines is significantly correlated with their human hal- delics (e.g., DOI, DOM, DOB, mescaline, LSD, and psilocin). In 1982, lucinogenic potency (Nelson et al., 1999). Studies have shown that the it was proposed that the mescaline-induced HTR is mediated by the 5-HT2B receptor is required for the releasing effects of the 5-HT releasers 5-HT2A receptor based on the fact that the relative potency of 5-HT DF and MDMA, and other findings argue that brain 5-HT2B receptors antagonists to block this behaviour is correlated with their affinity to may be involved in the cognitive and/or behavioural effects of psycho-

5-HT2A. Furthermore, non-hallucinogenic 5-HT2 receptor agonists such active drugs (Canal & Morgan, 2012). as lisuride and ergotamine do not induce this behavioural response. There is a consensus in the literature that the ability of DOI to induce

Thus, HTR seems to serve as a mouse bioassay that can predict the the HTR is not blocked by selective 5-HT2C receptor antagonists. There is hallucinogenic-specific signalling and effects of 5-HT2A receptor ago- some evidence that 5-HT2B/2C sites may play a modulatory role in this nists in humans. Numerous studies have shown that MDL100907 blocks behaviour. The non-selective 5-HT2B/2C receptor agonists Ro 60-0175, the HTR induced by hallucinogens. Mice lacking the 5-HT2A receptor MK-212, and mCPP do not induce the HTR in rats unless administered gene do not produce HTRs in response to mescaline, DOI, DOM, LSD, in combination with the 5-HT2C antagonist SB242084. There is also evi- DMT, 5-MeO-DMT, psilocin, or 1-methylpsilocin (Halberstadt, 2015), dence that the ability of DOI to induce the HTR is significantly attenuat- although the response can be rescued by selectively restoring the ed by pretreatment with 5-HT2B/2C agonists such as Ro 60-0175 and 5-HT2A receptor gene to cortical regions. mCPP. These findings indicate that 5-HT2C receptor activation reduces Interestingly, NMDA receptor antagonists including phencyclidine the manifestation of the HTR (Halberstadt, 2015). Likewise, DOI pro- (PCP)-like drugs also induce an HTR in rodents and enhance the duces a biphasic dose–response curve, and SB242084 reportedly shifts

5-HT2A-receptor-mediated HTR in mice (Nabeshima et al., 1987). In the descending arm of the DOI response to the right (Fantegrossi et al., animals, clozapine, ritanserin, amesergide, and ketanserin block PCP- 2010). Both the 5-HT2B/2C receptor selective antagonist/inverse agonist dependent locomotion and HTRs, which indicates a potential role of SB206553 and the 5-HT2C receptor antagonist SB242084 attenuate the circuits functioning through the 5-HT2 receptors to mediate the behav- HTR elicited by DOI in mice by 50%, and the DOI-induced HTR was atten- −/− ioural responses induced by NMDA antagonism. Similar results were uated by ~50% in Htr2C mice relative to their WT littermates (Canal & reported with the selective 5-HT2A receptor antagonist MDL100907. Morgan, 2012; Canal et al., 2010). Atypical antipsychotics reverse the cellular responses produced by In conclusion, both the 5-HT2B and 5-HT2C receptors modulate anti- PCP-like drugs in cortical pyramidal neurons and block the release of psychotic responses. Atypical antipsychotics behaving as 5-HT2A recep- 5-HT and glutamate in the prefrontal cortex. mGlu2 receptor activation tor inverse agonists might have efﬁcacy against negative symptoms abolishes the hallucinogen-speciﬁc signalling activated by LSD binding without evoking motor perturbation (Meltzer, 2013). Finally, with the to the 5-HT2A/mGlu2 receptor complex. Microdialysis experiments goal of exploiting ligand-directed signalling, 5-HT2A-receptor agonists in the cortex have demonstrated that extracellular glutamate levels in- favouring Gq versus Gi activation and devoid of hallucinogenic proper- crease more slowly than extracellular 5-HT levels after intraperitoneal ties are attractive possibilities for future drug discovery. administration of PCP-like drugs. These observations support that

5-HT and glutamate signalling through the 5-HT2A/mGlu2 receptor 3.2.6. 3.2.5. Prader–Willi syndrome complex might each be responsible for different LSD-like and PCP-like Prader–Willi syndrome (PWS) is caused by the loss of function of symptoms of schizophrenia (Gonzalez-Maeso et al., 2008). Serotonergic paternally expressed genes in the 15q11-q13 region. This region and glutamatergic drugs bind to the 5-HT2A/mGlu2 receptor hetero- contains the small nucleolar RNA (snoRNA) HBII-52, which exhibits complex, which then balances Gi- and Gq-dependent signalling. The sequence complementarity to the alternatively spliced exon Vb of

5-HT2A/mGlu2 receptor-mediated changes in Gi and Gq activity predict the 5-HT2C receptor. HBII-52 regulates the alternative splicing of the the psychoactive behavioural effects of a variety of pharmacological 5-HT2C receptor by binding to a silencing element in exon Vb. Prader– compounds (Fribourg et al., 2011). Prefrontal 5-HT2A receptor activation Willi syndrome patients do not express HBII-52 and have different by serotonin also enhances NMDA transmission and gates the induction 5-HT2C receptor mRNA isoforms compared to healthy individuals of temporal-dependent plasticity mediated by NMDA receptors at (Kishore & Stamm, 2006). Using whole genome microarrays to analyse thalamocortical synapses as observed in acute slices. Using a viral gene expression and quantitative RT-PCR analysis, alterations in the gene-delivery approach, expressing 5-HT2A receptors in the mediodorsal expression of serotonin receptor genes (e.g., HTR2B) and genes involved 24 L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36 in eating behaviour and obesity (e.g., ADIPOR2, MC2R, HCRT, OXTR)were calcineurin/NFAT (Vindis et al., 2010) pathway could be involved noted. Other genes of interest with reduced expression in PWS subjects in these regulatory actions by providing a pathophysiological role of included STAR (a key regulator of steroid synthesis) and SAG (an 5-HT in cardiac hypertrophy. In adult humans, 5-HT2B receptors were arrestin family member that desensitizes G protein-coupled receptors). also found to be overexpressed in the hearts of patients with congestive Quantitative RT-PCR data of SAG, OXTR, STAR, HCRT, and HTR2B levels heart failure, and this overexpression was positively correlated with using RNA isolated from the lymphoblastoid cells and available brain cytokine and norepinephrine plasma levels (Jaffre et al., 2009). Seroto- tissue (frontal cortex) from either individuals with PWS or control sub- nin plasma levels are also increased in patients with heart failure and jects were normalized to GAPDH gene expression levels and validated in animal models of cardiac hypertrophy induced by aortic constriction. themicroarraygeneexpressiondata(Bittel et al., 2007). These ﬁndings may indicate that 5-HT induces cardiac hypertrophy or

heart failure through the 5-HT2B receptor. The 5-HT2B receptor has 3.3. Cardiovascular system been shown to be involved in cardiac hypertrophy by acting directly on cardiac myocytes. After two weeks of aortic banding surgery,

Expression of the 5-HT2C receptors in the cardiovascular system is mRNA and protein expression of 5-HT2B receptors signiﬁcantly in- undetectable. creased. The antagonist SB215505 signiﬁcantly reduced the increase in heart weight, heart wall thickness, left ventricular mass, and the expres- 3.3.1. Heart failure and cardiac hypertrophy sion of the brain natriuretic peptide (BNP) but did not attenuate the

Both the 5-HT2A and 5-HT2B receptors have been implicated in cardi- upregulation of 5-HT2B receptor protein expression in rats after aortic ac hypertrophy and failure and are expressed on the cardiomyocyte banding. Following in vitro mechanical stretching of cardiomyocytes cell surface. 5-HT2A receptor activation triggers positive ionotropic and incubation with 5-HT, the level of 5-HT2B receptors and BNP protein responses (Brattelid et al., 2007). Noteworthy, despite a similar coupling increased in a temporal-dependent manner. When transfected with to the 5-HT2A receptor subtype, 5-HT2B receptor stimulation does specific siRNA against 5-HT2B receptors, cardiomyocytes showed a not elicit any contractile response, although the response to the reversal of the 5-HT-induced increase in NF-κB translocation and BNP −/− β-adrenergic receptor agonist dobutamine in Htr2B cardiomyocytes protein as well as in the mechanical stretching (Liang et al., 2006). was impaired (Nebigil et al., 2001). Serotonin binding to the Gq- By mimicking sympathetic stimulation in vivo, mice globally lacking coupled 5-HT2B receptor protects cardiomyocytes against serum serotonin 5-HT2B receptors did not develop isoproterenol-induced left deprivation-induced apoptosis, which is detected by DNA fragmentation, ventricular hypertrophy (Jaffré et al., 2004). The exact cardiac cell nuclear chromatin condensation, and TUNEL labelling. Serotonin prevents type(s) expressing 5-HT2B receptors (cardiomyocytes versus non- cytochrome c release and activation of caspase-9 and caspase-3 after cardiomyocytes) involved in this pathological cardiac hypertrophy serum deprivation via cross-talk between the phosphatidylinositol-3 was addressed in vivo: mice with conditional expression of 5-HT2B kinase/Akt and extracellular signal-regulated kinase ERK1/2 signalling receptor in cardiomyocytes, such as global 5-HT2B receptor-null mice, pathways. Serotonin binding to the 5-HT2B-receptor activates ERK kinases are resistant to isoproterenol-induced cardiac hypertrophy and dys- to inhibit the expression of Bax induced by serum deprivation. Serotonin function as well as to isoproterenol-induced increases in plasma cyto- signalling via the phosphatidylinositol-3 kinase/Akt pathway can activate kine levels (Jaffre et al., 2009), which points to a fibroblast effect. In NF-kB, which is required for the regulation of the mitochondrial adenine primary cultures of cardiac fibroblasts, angiotensin II and isoproterenol nucleotide translocator (ANT-1). Parallel to these observations, stimulated NOX activity that was prevented by a selective antagonist −/− ultrastructural analysis of Htr2B mouse hearts revealed pronounced (SB215505). 5-HT2B receptor blockade by SB215505 prevented the mitochondrial defects in addition to altered mitochondrial enzyme increase in cardiac superoxide generation and hypertrophy in two activities (i.e., cytochrome oxidase and succinate dehydrogenase) mouse models of cardiac hypertrophy, i.e., angiotensin II and isoproter- and ANT-1 and Bax expression levels. These findings identify 5-HT as enol infusions (Monassier et al., 2008). A functional interaction between a novel survival factor targeting the mitochondria in cardiomyocytes the AT1 and 5-HT2B receptors via a transinhibitory mechanism that may via 5-HT2B receptors (Nebigil et al., 2003). involve heterodimeric receptor complexes was shown to trigger cyto- A cardioprotective role of the 5-HT2A receptor blockade was also kine release in cardiac fibroblasts (Jaffre et al., 2009)andcouldbea recently suggested by Blasco-Fontecilla et al. (2010). These authors new therapeutic target. emphasized that atypical antipsychotic drugs could reduce the risk of The involvement of 5-HT2B receptors was reported in the generation cardiovascular events in patients with schizophrenia. In fact, the cardio- of apoptotic events associated with cardiac remodelling during in- vascular risk is increased in these patients due to cigarette smoking, creased adrenergic stimulation (Bai et al., 2010). Based on these data, metabolic disorders and cardiac arrhythmias caused by QT prolonga- the effect of a chronic 5-HT2B receptor blockade by the selective antag- tion. Independent of lifestyle, some of these issues can be favoured onist RS127445 was investigated in spontaneously hypertensive rats by antipsychotics themselves but interestingly, Tiihonen et al. (2009) showing left ventricular hypertrophy in conjunction with diastolic dys- suggested that long-term exposure to antipsychotics could reduce over- function and an apparently normal ejection fraction (Ayme-Dietrich all cardiovascular mortality, with the best profile obtained for anti- et al., 2015; Marzak et al., 2014). In this model, the 5-HT2B receptor is psychotic drugs having higher 5-HT2 receptor affinity, i.e., clozapine, overexpressed in the left ventricle, but the antagonist did not improve quetiapine, olanzapine, and thioridazine. It is quite difficult to identify either cardiac function or the hypertrophy. An increase in subendocar- a mechanism in such epidemiological studies, but a reduction of platelet dial ventricular fibrosis was observed and was reproduced by 5-HT −/− aggregation and thrombus formation combined with a limitation of injections in WT mice but amplified in Htr2B animals. Therefore, in coronary spasms, both of which are linked with 5-HT-mediated 5- hypertensive cardiomyopathy, 5-HT2B receptors could also be associat- HT2A receptor activation, could contribute to cardiovascular protection ed with cardioprotection through endothelial-mediated coronary vaso- in these patients. dilatation (Ayme-Dietrich et al., 2015).

Another role of cardiac 5-HT2 receptors is myocardial hypertrophy. These data revealed a dual role of 5-HT2A/2B receptors on both Genetic studies failed to show any genetic polymorphisms in the cardiomyocytes and cardiac ﬁbroblasts in regulating cardiac hypertro-

5-HT2A receptor gene in patients with hypertrophic cardiomyopathy phy in vivo. either of genetic origin or due to hypertension. Conversely, the expression of this receptor is increased in patients with cardiac hypertrophy, 3.3.2. Pulmonary arterial hypertension and pharmacological inhibition can prevent the development of Pulmonary arterial hypertension (PAH) is a progressive and cardiac hypertrophy induced by transverse aortic constriction in mice often fatal disorder in humans that results from an increase in pul- (Lairez et al., 2013). Caveolin-3 (Mialet-Perez et al., 2012) and the monary blood pressure associated with abnormal vascular proliferation. L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36 25

Serotonin has been associated with the pathogenesis of PAH (Chan & Therefore, in some conditions, a 5-HT2A receptor stimulation could Loscalzo, 2008). Therapeutic drugs that exert PAH as a side effect, sensitize smooth muscle cells towards vasodilation triggered by other such as the amphetamine derivative and anorexigen dexfenﬂuramine, serotonergic receptors. can act as potent 5-HT releasers acting at SERT and/or agonists at Aside from its contribution to vasomotion, 5-HT2A receptors also 5-HT2B receptors (Weir et al., 2008). Blockade of 5-HT2B receptors appear to be key contributors to atherosclerosis and arterial wall −/− using independent approaches (i.e., genetic ablation (Htr2B )or remodelling. In rabbits fed a high cholesterol diet, sarpogrelate reduced pharmacologic inactivation (5-HT2B receptor antagonist RS127445)) the extent of atherosclerotic deposits in the aorta in parallel to induced completely prevented the development of hypoxia-induced pulmonary endothelial nitric oxide synthase expression (Hayashi et al., 2003). hypertension in mice, including the increase in pulmonary blood pres- These chronic effects combined with a reduction of 5-HT- and angioten- sure and lung remodelling, the increase in vascular proliferation, in- sin II-induced vascular smooth muscle cell proliferation (Sharma et al., creased elastase activity and elevated transforming growth factor-β-1 2001; Watanabe et al., 2001) could limit vascular remodelling. This (TGFβ1) levels (Launay et al., 2002). Using the monocrotaline-induced effect is now clear in peripheral arterial disease, as sarpogrelate pulmonary hypertension model, recent studies conﬁrmed that other improves the outcome of symptomatic patients (Ren et al., 2013), but

5-HT2B receptor antagonists (e.g., terguride, PRX-08066, and C-122) this effect remains to be demonstrated after endovascular therapy. significantly reduced pulmonary pressure, arterial wall thickening, and Retrospective studies showed a reduction of major clinical endpoints lumen occlusion but maintained cardiac function (Porvasnik et al., such as amputation or death from any cause after endovascular therapy 2010; Dumitrascu et al., 2011; Zopf et al., 2011). Pulmonary hyperten- for patients with critical hind limb ischaemia (Takahara et al., 2014), sion is associated with a substantial increase in 5-HT2B receptor expres- and the first preliminary results of a recent prospective study suggest sion in the pulmonary arteries of rodents and humans (Launay et al., that sarpogrelate coadministered with aspirin is as efficacious as

2002; Dumitrascu et al., 2011). Therefore, activation of 5-HT2B receptors sarpogrelate coadministered with clopidogrel for the prevention of re- appears to be a limiting step in the development of pulmonary hyperten- stenosis following femoropopliteal arterial stenting (Chen et al., 2015). sion. Recently, the restricted expression of 5-HT2B receptors to bone The reduction of neointimal hyperplasia in combination with the marrow cells was shown to be necessary and sufﬁcient for the develop- improvement of endothelial function after sarpogrelate treatment ment of pulmonary hypertension in response to either hypoxia or mono- (Miyazaki et al., 2007) highly encourages its use in patients with periph- crotaline (Launay et al., 2012). eral arterial disease and emphasizes the contribution of the 5-HT2A These ﬁndings reveal a limiting role of 5-HT2B receptors in PAH receptor in chronic artery disease. development and shift the contribution of 5-HT to PAH to an extra- Diabetes mellitus is a pathological situation that puts patients at high pulmonary, haematopoietic event and open new possibility for thera- risk for cardiovascular events. In an experimental model of type 2 diabe- peutic interventions. tes, 5-HT increases plasma epinephrine and glucose levels, making rats

insulin resistant. This resistance involves 5-HT2A receptors because these increases are blocked by sarpogrelate pretreatment (Takishita 3.3.3. Vascular tone of systemic and coronary arteries et al., 2004). The insulin-sensitizing effect of sarpogrelate has been The pharmacology of 5-HT in systemic arteries is complex. 5-HT confirmed in diabetic patients (Kokubu et al., 2006) and in mice when can elicit vasoconstriction through its interaction with 5-HT2A recep- combined with the PPAR-γ agonist pioglitazone (Iizuka et al., 2009). tors on vascular smooth muscle cells but can also induce vasodilata- High glucose levels promote endothelial dysfunction, and 5-HT has tion via a nitric oxide-dependent mechanism involving 5-HT1B/2B been suggested as a key pathophysiological player in the vascular com- receptors. In the coronary circulation, the effects of the 5-HT2A plications of diabetes in the context of metabolic syndrome. When rat receptor-selective antagonist sarpogrelate were investigated in aortic rings are incubated in a solution with a high glucose concentra- dogs subjected to an acute reduction of the coronary blood flow tion, the endothelium-dependent vasodilatation triggered by acetylcho- (30% of the baseline flow) in the anterior wall (Fujita et al., 2004). line is reduced, whereas the endothelium-independent dilatation

Sarpogrelate ampliﬁed 5-HT release in the myocardium and 5-HT1B induced by an NO donor is unaffected. Interestingly, sarpogrelate can re- receptor-mediated dilatation via NO synthase. Such a mechanism store endothelial NO production and, as a consequence, NO-mediated was also suggested in an ischaemic hind limb model in diabetic mice dilatation (Sun et al., 2011). Nevertheless, these effects were obtained in which sarpogrelate restored perfusion through 5-HT1B receptor- at high sarpogrelate concentrations (10 μM) in a culture medium in mediated stimulation of the eNOS/Akt pathway (Iwabayashi et al., which the concentration of 5-HT was not measured. This work empha-

2012). Nevertheless, an effect in the absence of 5-HT could also occur sizes that blocking 5-HT2A receptors could protect endothelial function due to the inverse agonist action of this drug (Muntasir et al., in diabetic patients. In a rat model of type 1 diabetes, sarpogrelate 2006; Hossain et al., 2012). In humans, a single 200 mg oral dose of reduced blood glucose levels and endothelial PECAM-1 overexpression, sarpogrelate also increased the basal and maximal (in response to aden- thereby limiting 5-HT-induced thrombosis (Yamada et al., 2012). Inter- osine triphosphate) average peak velocity of coronary blood ﬂow in estingly, this receptor also affects neointimal proliferation and resteno- patients with coronary artery disease. These changes in vasodilatation sis following arterial stenting, although the 5-HT2A receptor is not were also observed in rabbit cerebral arteries (Kawamura et al., 2013) expressed on endothelial cells. Either a paracrine mechanism involving and in experimental vein grafts (Kodama et al., 2009). The mechanisms cytokines released by smooth muscle cells or the regulation of the of these sarpogrelate effects are not fully understood. A novel vasodila- homing of circulating cells could explain some of the vascular beneﬁcial tion response linked to 5-HT-induced 5-HT1B receptor stimulation is effects following 5-HT2A receptor blockade. one possible explanation, but other mechanisms have been proposed. Taken together, these data all argue in favour of a major contribution

In rats chronically treated with sarpogrelate, serotonergic stimulation of the 5-HT2A receptor in the regulation of vasomotor tone and in the of the 5-HT7 and 5-HT1D receptors counteracts the pressure response interaction between endothelial and smooth muscle cells trough a elicited by sympathetic nervous system stimulation (Garcia-Pedraza subtle equilibrium involving other receptors. et al., 2014). This phenomenon involves smooth muscle cell hyperpo- 5-HT2B receptors are also involved in vascular responsiveness during larization and the COX2 pathway. Interestingly, 5-HT can induce hypertension. Mesenteric arteries from deoxycorticosterone (DOCA)-

5-HT2A receptor-mediated COX2-dependent prostacyclin synthesis salt hypertensive rats predominantly contract via 5-HT2B receptors. in smooth muscle cells via the PKC/Src/MAPK pathway. This biological PCR analyses indicate an increase in 5-HT2B receptor mRNA levels in effect could be involved in vasodilatation and implicates the 5-HT2A the mesenteric arteries of DOCA-salt hypertensive arteries, suggesting receptor because this effect is antagonized by sarpogrelate (Machida an increase in receptor number (Watts et al., 1996). The endothelium- et al., 2011). denuded isolated superior mesenteric arteries of DOCA-salt rats display 26 L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36

a marked increase in maximum contraction to the 5-HT2B receptor ago- valve regurgitation has been associated with increased mRNA expres- nist BW723C86 compared with the response of arteries from sham rats, sion of valvular 5-HT2B receptors and SERT in pigs (Cremer et al., confirming that the 5-HT2B receptor plays a greater role in 5-HT- 2015a). Canine myxomatous mitral valve disease was associated with induced contraction in the arteries from DOCA-salt rats. In chronically higher expression of 5-HT2B receptors in the mitral valve (Cremer instrumented rats, the 5-HT2B receptor antagonist LY272015 signifi- et al., 2015b). cantly reduced the mean blood pressure (Watts & Fink, 1999). These findings suggest that 5-HT2B signalling links vascular damage LY272015 produced a 4-fold rightward shift to 5-HT in the aortas and platelet activation to tissue remodelling and identifies 5-HT2B as a from hypertensive rats exposed to the nitric-oxide synthase inhibitor novel therapeutic target to treat valvular heart diseases.

N(omega)-nitro-L-arginine indicating that 5-HT2B receptors are overexpressed and contribute to the high blood pressure in these animals 3.3.5. Migraine (Russell et al., 2002). A role for 5-HT in migraines has been supported by changes in

These ﬁndings reveal that the 5-HT2B receptor plays an important the circulating levels of 5-HT and its metabolites during the phases of role in 5-HT-induced contraction in arteries of hypertensive individuals a migraine attack. A migraine headache is thought to be transmitted who could be targeted for therapeutic purposes. from the meninges and their associated blood vessels by the trigeminal nerve. Correlation of the receptor afﬁnities with the potencies used

3.3.4. Valvular heart disease in migraine prophylaxis showed signiﬁcant correlations for the 5-HT2B Carcinoid heart disease occurs in over 65% of patients with carcinoid receptor. Various human meningeal tissues express 5-HT2B mRNA syndrome and is characterized by ﬁbrous thickening of cardiac valves, (Schmuck et al., 1996). The 5-HT2B receptor can activate the release of leading to heart failure (Roth, 2007). A correlation of high plasma NO and induce the relaxation of the cerebral arteries and jugular vein.

5-HT levels with valvular abnormalities detected by cardiac catheteriza- 5-HT2B receptors located in the endothelial cells of meningeal blood tion and echocardiography has been reported. Thus, 5-HT overproduc- vessels may trigger migraine headache through the formation of NO, tion has been proposed to be responsible for cardiac valvular disease which results in the dilation of cerebral blood vessels and the concomi- in patients with carcinoid tumours (Robiolio et al., 1995). The similarity tant activation of sensory trigeminovascular afferents, thus initiating to lesions in carcinoid heart disease and in methysergide-associated val- the manifestation of head pain (Schmuck et al., 1996; Johnson et al., vular disease suggested direct stimulation of myofibroblast growth by 2003). In addition, a recent genetic study identified 5-HT2B receptors 5-HT agonism (Hendrikx et al., 1996). The occurrence of fenfluramine- as a gene susceptible to migraine (Corominas et al., 2010). associated valvular heart disease has raised concerns that other seroto- Endothelial 5-HT2B receptors may thus trigger the dilation of menin- nergic medications might also increase the risk of developing valvular geal blood vessels which, by activating sensory trigeminovascular affer- heart disease (Connolly et al., 1997). Dexfenfluramine was approved ents, induces head pain. in the United States for long-term use as an appetite suppressant until it was reported to be associated with valvular heart disease. The valvular 3.4. Cancer changes (e.g., myofibroblast proliferation) are histopathologically indis- tinguishable from those observed either in patients with carcinoid In addition to its numerous physiological functions, 5-HT has been disease or after long-term exposure to 5-hydroxytryptamine 5-HT2- shown to be a mitogenic factor in a wide range of normal and tumour preferring ergot drugs (e.g., ergotamine, methysergide). The amphet- cells. The following section will emphasize the role of 5-HT2 receptors amine derivative MDMA and its metabolite MDA each preferentially in cancer. bind to and activate human recombinant 5-HT2B receptors and, similar to fenfluramine and its N-demethylated metabolite norfenfluramine, 3.4.1. Carcinoid tumours elicit mitogenic responses in human valvular interstitial cells via activa- 5-HT2B receptor expression was observed in spontaneous human ras tion of 5-HT2B receptors (Setola et al., 2003). carcinoid tumours along with coupling to p21 activation, ERK1/2 Based on strikingly similar echocardiographic and histopathological activation, and proliferation (Launay et al., 1996; Nebigil et al., 2000). features, it is now considered that ergot-derived dopamine agonists The proliferative activity of small intestinal neuroendocrine tumours may cause valvular heart diseases nearly identical to that observed (including cell growth and the development of desmoplasia) is associat- in patients with carcinoid syndrome (Horvath et al., 2004). Population ed with the particular microenvironment in the peritoneum, and studies of patients with Parkinson's disease compared to non- tumour cells support this necessary milieu through the secretion of parkinsonian controls have reported that pergolide and cabergoline profibrotic/angiogenetic factors (Svejda et al., 2010), but autocrine have a similar risk of inducing fibrotic changes in cardiac valve leaflets. activity of 5-HT/5-HT2B receptors is likely. Pergolide and cabergoline have a high affinity for the 5-HT2B receptor. The frequency of moderate-to-severe regurgitation in at least one 3.4.2. Breast tumours heart valve was higher in patients receiving either cabergoline or The increased biosynthetic capacity of 5-HT accompanied by multi- pergolide than in patients taking either non-ergot agonists or controls, ple changes in 5-HT receptor expression and signalling favours the and the incidence of new-onset valvulopathy was high in patients malignant progression of human breast cancer cells (e.g., stimulated taking ergot-derived drugs (Antonini & Poewe, 2007; Roth, 2007). proliferation, inappropriate cell survival). Expression levels of the

Simultaneous mitral bioprostheses hypertrophic scaring and native 5-HT1F, 5-HT2B, 5-HT2C, 5-HT5A, and 5-HT7 receptors show an overall aortic valve fibrosis was recently reported during benfluorex therapy increase in breast cancer. Among these receptors, 5-HT2B receptor in a 40-year-old woman. The bioprostheses and aortic valves exhibited expression was found to be increased in breast cancers, and HTR2B similar histopathological lesions. Thickening and plaque deposits made mRNA is also expressed in untransformed human mammary epithelium by smooth muscle α-actin- and vimentin-positive cells in a glycosami- (Pai et al., 2009). HTR2B mRNA expression was found to be lower noglycan matrix were observed, which supported that activation by in oestrogen receptor (ER)-negative basal tumours compared with the 5-HT2B receptor agonist norfenfluramine (also a metabolite of luminal tumours, which are most commonly ER-positive. HTR2B mRNA benfluorex) triggers the development of drug-induced heart disease was elevated in carcinomas, increased with tumour stage, and concom-

(Ayme-Dietrich et al., 2012). 5-HT2B and 5-HT2A receptor transcripts itantly higher in lymph node-positive tumours compared to lymph are easily detected in heart valves while no 5-HT2C receptor transcript node-negative tumours. This observation was supported by a study is detectable. Preferential stimulation of valvular 5-HT2B receptors showing that c-Myc transformation induced an increase in HTR2B (with or without accompanying 5-HT2A receptor activation) may con- expression (Pai et al., 2009). In human breast cancer, an analysis re- tribute to valvular ﬁbroplasia in humans (Fitzgerald et al., 2000). Mitral vealed a signiﬁcant correlation of HTR2B with ER-α (Kopparapu et al., L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36 27

2013). Although 5-HT2A receptor expression was detected in a human demonstrate novel insights of 5-HT activity in cancer biology and sug- breast cancer cell line (MCF-7) and pegged as responsible for the mito- gest 5-HT-mediated signalling as a therapeutic target (Soll et al., genic effect of 5-HT, these preliminary data have not been conﬁrmed 2010). The 5-HT1B and 5-HT2B receptors were expressed, respectively, (Sonier et al., 2006). in 32% and 35% of patients with hepatocellular cancer. Both receptors were associated with an increased proliferation index (Soll et al.,

3.4.3. Melanomas 2012). The 5-HT2B receptor mediates 5-HT-induced proliferation Uveal (ocular) melanoma is an aggressive cancer that often forms in serum-deprived HCC Huh7 cells. Additionally, inhibition of the undetectable micrometastases before diagnosis of the primary tumour. 5-HT2B receptor in Huh7 cells using SB204741, a selective 5-HT2B recep- High increases in HTR2B mRNA transcript levels were found in all uveal tor antagonist, signiﬁcantly decreased the expression of FOXO3a, melanomas with monosomy 3 compared with low expression in all demonstrating that FOXO3a was a target of 5-HT in Huh7 cells (Liang tumours with disomy 3. As monosomy 3 is associated with metastatic et al., 2013). disease, HTR2B expression has been proposed as a marker to identify patients with a poor prognosis (Tschentscher et al., 2003). The 5-HT2B 3.4.7. Choriocarcinoma receptor signals through the heterotrimeric GTPase GNAQ, which is This gestational trophoblastic disease is due to abnormal growth of mutated in half of uveal melanomas (Onken et al., 2010). The 5-HT2B trophoblast cells. 5-HT2A receptor expression was found in human cho- receptor is one of the highest overexpressing genes in class 2 uveal mel- riocarcinoma cell lines such as JEG-3 and BeWo as well as in normal anomas (van Gils et al., 2008). A PCR-based 15-gene assay comprising human placental tissue. 5-HT stimulation leads to a concentration-

12 discriminating genes including HTR2B are now part of a prognostic dependent increase in proliferation of choriocarcinoma cell lines with assay, which provides an important addition to the armamentarium a maximal increase in JEG-3 cell proliferation of 25.6 ± 6.8% with for managing patients with uveal melanoma (Onken et al., 2010). 40 μM of 5-HT and 11.1 ± 4% with 20 μM of 5-HT for BeWo cells com-

These genes, including HTR2B, help to distinguishing whether uveal pared to untreated control cells (Sonier et al., 2006). The same research melanomas contain liver metastases and thus aid in the diagnosis and group conﬁrmed the role of 5-HT2A receptor in cell viability and cell prevention of uveal melanoma liver metastases based on the differential cycle progression by treating JEG-3 and BeWo cells with the 5-HT2 re- expression patterns (Zhang et al., 2014). ceptor agonist DOI and reversing the concentration-dependent increase

in cell viability with ketanserin, a 5-HT2A receptor-selective antagonist. 3.4.4. Prostate cancer Moreover, stimulation of 5-HT2 receptors by DOI in these two choriocar- Prostate cancer is the most commonly diagnosed non-cutaneous cinoma cell lines activated both the MEK-ERK1/2 and JAK2-STAT3 cancer in men. Despite this fact, many of the genetic changes that coin- signalling pathways (Oufkir et al., 2010). cide with prostate cancer progression remain enigmatic. The 5-HT2B receptor was found to be upregulated in tumours relative to benign 3.4.8. Glioma glands (Magee et al., 2001). Overstimulation of receptors in response Human malignant gliomas are particularly invasive, which makes a to neuroendocrine cell products has been suggested to contribute to complete surgical resection very difﬁcult. Therefore, pharmacological the development of hormone-refractory prostate cancer. Immunostain- approaches are necessary. Merzak et al. (1996) identiﬁed 5-HT2 recep- ing for the 5-HT2B receptor was observed in low-grade and high-grade tor expression by RT-qPCR in eight glioma cell lines and weak expres- tumours, prostatic intra-epithelial neoplastic and benign prostatic sion in normal foetal astrocytes originating from the cerebellum and hyperplasia cells, and vascular endothelial cells. Antagonists at the the left hemisphere. Moreover, these authors showed that 5-HT stimu-

5-HT2B receptor have been reported to inhibit the proliferation of pros- lates the proliferation, migration, and invasion of glioma cells. Never- tate cancer cells in a dose-dependent manner (Dizeyi et al., 2005). theless, they were unable to clearly establish the receptor subtype involved. Other in vitro experiments performed in rat astrocytes

3.4.5. Adrenocortical carcinoma and 9L glioma cells detected 5-HT2A receptor expression by RT-qPCR Interestingly, gene expression profiles of adrenocortical tumours among the twelve 5-HT receptor subtypes explored (Sarrouilhe et al., identified the underexpression of HTR2B mRNA as a marker of malig- 2015). In this work, 5-HT stimulation of C6 glioma cells increased glial nant adrenocortical carcinoma (Fernandez-Ranvier et al., 2008). fibrillary acidic protein (GFAP) expression at the mRNA and protein Analysis of the biomarkers of malignant adrenocortical cancers in a levels, suggesting that 5-HT could induce the differentiation of these meta-analysis has revealed that the combination of overexpressed cells (Morita et al., 2006). Finally, stimulation of C6 glioma cells with anillin (ANLN) and underexpressed HTR2B mRNA levels appeared to 5-HT increased the release of glial cell line-derived neurotrophic factor be the best predictor of malignancy (Zsippai et al., 2011). However, (GDNF), an effect that was blocked by treatment with either ketanserin in adrenocorticotropin-dependent adrenal hyperplasias, the mechanisms or cyproheptadine. These results suggest that 5-HT2A receptors could be responsible for the ectopic adrenal expression of glucose-dependent involved in the survival, proliferation and migration of glioma cell lines insulinotropic peptide (GIP) receptor (GIPR) in GIP-dependent Cushing's via GDNF release (Hisaoka et al., 2004; Tsuchioka et al., 2008). syndrome are unknown. Chronic adrenal stimulation by GIP in GIP- dependent ACTH-independent macronodular adrenal hyperplasia leads 3.4.9. T cell leukaemia to a significant induction of GPR54, HTR2B, GPR4, and the endothelial The proteasome inhibitor bortezomib could be a potential therapeu- differentiation sphingolipid receptor EDG8 (Lampron et al., 2006). tic agent in treating adult T cell leukaemia (ATL) patients. A network

that includes HTR2B was identiﬁed and converges on the secreted pro- 3.4.6. Hepatocellular carcinoma tein acidic and rich in cysteine (SPARC) gene, a tumour-invasiveness Among the 64 genes for which mRNA expression levels differed related gene, which may act as a possible modulator of bortezomib- between hepatitis C-type hepatocellular carcinoma (HCC) and either induced cell death in ATL cells (Ohyashiki et al., 2008), although the the non-hepatitis B-type or non-hepatitis C-type, the most affected putative role of 5-HT was not investigated. gene found was HTR2B (Iizuka et al., 2004). The function of 5-HT as a survival factor of HCC cells was recently demonstrated: activation of 3.4.10. Osteosarcoma the 5-HT2B receptor leads to sustained phosphorylation of the two Htr2A mRNA is found in anaplastic osteoblasts as well as in differen- downstream targets of mTOR, p70S6K and 4E-BP1, thereby facilitating tiated and matured osteoblasts, whereas Htr2B mRNA is only expressed survival and inhibiting autophagy. Inhibiting the 5-HT2B receptor re- in differentiated and matured osteoblasts (Westbroek et al., 2001; Hirai duced cancer cell growth in vitro and in vivo. The presence of 5-HT2B et al., 2009). The 5-HT2A receptor has been shown to regulate MC3T3-E1 receptors in HCC and the activation of autophagy-related mechanisms osteoblast cell proliferation by activating the ERK pathway. This effect is 28 L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36

reversed by the 5-HT2A receptor-selective antagonist ketanserin (Hirai coupled to the PLA2 pathway and prostaglandin production at the et al., 2009, 2010). Bracha et al. (2013) reported the serotonergic signal- beginning of mineral deposition. The 5-HT2B receptor also controlled ling pathway triggered by the 5-HT2A receptor in non-neoplastic canine leukotriene synthesis via PLA2 during the terminal stages of differentia- osteoblasts and in an osteosarcoma cell line. This group demonstrated tion. These two 5-HT2B receptor-dependent eicosanoid productions that the intracellular second messenger signal is different between nor- delineate distinct snapshots of TNAP regulation during osteogenic pro- mal and malignant osteoblast cells: ritanserin, a 5-HT2 receptor antago- gramming. Finally, either prostaglandins or leukotrienes were shown nist, decreased ERK phosphorylation and cell viability in non-neoplastic to relay the post-translational activation of TNAP via stimulation of the osteoblasts cell lines, whereas this compound decreased cell viability via phosphatidylinositol-speciﬁc phospholipase C. In agreement with the −/− CREB phosphorylation in osteosarcoma cell lines. The lack of selectivity above ﬁndings, primary calvarial osteoblasts from Htr2B mice were of the 5-HT2 antagonists used precludes any conclusion about the exact shown to exhibit defects in TNAP activity (Baudry et al., 2010). Brain receptor involved in this observed activity. 5-HT was proposed to indirectly favour the accrual of bone mass follow-

ing activation of 5-HT2C receptors on ventromedial hypothalamic neu- 3.4.11. Myosarcoma rons and 5-HT2B receptors on arcuate neurons (Yadav et al., 2009). In the pathogenesis of uterine leiomyosarcoma, a cDNA microarray Compared to control osteoblasts, the lack of 5-HT2B receptors was analysis identified a fourfold overexpression of HTR2B among the most associated with a 10-fold overproduction of prostacyclin (PGI2). Addi- overexpressed genes (Arslan et al., 2005; Matsumura et al., 2006). tionally, a specific prostacyclin synthase inhibitor (U51605) completely −/− rescued osteoblast aggregation and matrix mineralization in Htr2B 3.4.12. Tumour angiogenesis osteoblasts without having any effect on WT osteoblasts. Prostacyclin −/− In tumour-infiltrating macrophages, 5-HT does not enhance colon is the endogenous ligand of PPAR-β/δ, and its inhibition in Htr2B cancer tumour cell proliferation but may act as a regulator of angiogen- cells completely rescued the mRNA levels of alkaline phosphatase esis by reducing the expression of MMP-12, which results in lower and osteopontin, cell–cell adhesion, and matrix mineralization. The levels of angiostatin—an endogenous inhibitor of angiogenesis (Nocito absence of 5-HT2B receptors leads to the overproduction of prostacyclin, et al., 2008). Serotonin can stimulate the phosphorylation of ERK1/2 in which results in reduced osteoblast differentiation due to peroxisome bovine endothelial cells, and the 5-HT2B receptor was reported to play proliferator-activated receptor (PPAR)-β/δ-dependent target regu- a role in the activation of eNOS in human endothelial cells. In lation and defective cell–cell adhesion and matrix mineralization

SB204741-treated mice, the selective blockade of the 5-HT2B receptor (Chabbi-Achengli et al., 2013). HTR2A was also found to be expressed resulted in the reduction of tumour angiogenesis and growth through only in osteoblasts, whereas HTR2B expression increased from precursor the inhibitory effect of ERK1/2 and eNOS (Asada et al., 2009). Therefore, to mature osteoclasts (Hodge et al., 2013). A recent study highlights the the possibility that 5-HT2B receptors participate in tumour angiogenesis contribution of the 5-HT2A receptor in bone metabolism. This receptor is likely but requires further evaluation in other tumour subtypes. appears involved in osteoblast differentiation and bone mineral density.

In conclusion, the contribution of 5-HT2 receptors in tumours Blocking 5-HT2A receptor signalling by MDL11939 decreased bone mass remains to be determined but is dependent on the tumour type. and led to skeletal fragility in mice. Moreover, the pharmacological

blockade of 5-HT2A receptors signiﬁcantly decreased cellular differenti- 3.5. Skeleton ation in MC3T3-E1 cells and osteoblast primary cultures from the right femur of mice (Tanaka et al., 2015).

3.5.1. Bone development and osteoporosis All these results drive to the hypothesis that 5-HT and the 5-HT2A/2B Although Htr2B mRNA is undetected in anaplastic osteoblasts, it receptor signalling pathways may contribute to bone formation and appears in differentiated and matured osteoblasts (Bliziotes et al., cellular differentiation. 2001; Westbroek et al., 2001). The differentiation and maturation of osteoblasts might thus be regulated by activation of the 5-HT2B receptor 3.5.2. Tooth development −/− (Hirai et al., 2009). Of interest, Htr2B female mice displayed signifi- Periodontal diseases occur in patients treated with antidepressants −/− cantly reduced bone density from the age of 4 months, which was inten- such as SSRIs (e.g., Prozac), which target SERT. In the molars of Htr2B sified at 12 and 18 months. This finding histomorphometrically mice, rod curvatures and twisting were altered compared to WT confirmed that osteopenia was due to reduced bone formation since mice, suggesting the involvement of Htr2B at early stages of enamel −/− (i) the alkaline phosphatase-positive colony-forming unit capacity of formation. The volume of the Htr2B enamel layer was also reduced, −/− bone marrow precursors was markedly reduced in Htr2B mice from with smaller crystallite thickness. The outer aprismatic enamel border −/− −/− 4 to 12 months of age, (ii) ex vivo primary osteoblasts from Htr2B was 1.5- to 2-fold larger in Htr2B mice compared to WT mice. Finally, mice exhibited reduced proliferation and delayed differentiation, and although no noticeable difference was observed in dentin, the three- (iii) calcium incorporation was markedly reduced in osteoblasts after dimensional pulp reconstruction suggested a decrease in both the −/− 5-HT2B receptor depletion (produced either genetically or by pharmaco- length and width of dentin formation in the root canals of the Htr2B logical inactivation) (Colletetal.,2008). Using the osteoprogenitor cell mice versus WT mice (Dimitrova-Nakov et al., 2014). line C1, blockade of the intrinsic activity of the 5-HT2B receptor was Therefore, 5-HT2B receptors may mediate some harmful effects of reported to affect the mineralization efficiency by decreasing calcium the long-term use of SSRIs on bone and teeth regeneration. incorporation. Optimal bone matrix mineralization involves both NO and PLA2 signalling pathways, and the 5-HT2B receptor promotes pros- 4. Emerging research and new therapeutic opportunities taglandin E2 production through cyclooxygenase (COX) activation. When C1 osteoblasts undergo conversion into osteocyte-like cells, 4.1. Haematopoiesis

COX activity was quenched. The 5-HT2B receptor contributed to osteogenic differentiation in an autocrine manner (Locker et al., 2006). A In addition to its role as a neurotransmitter, 5-HT has been shown functional link between the 5-HT2B receptor and the activity of tissue to regulate inflammation and tissue repair via a set of receptors whose non-specific alkaline phosphatase (TNAP) was established. Agonist expression pattern varies among cell lineages. Previous studies have stimulation of the receptor increased TNAP activity during the initial shown that 5-HT is a growth factor for haematopoietic stem/progenitor mineralization phase. Indeed, inhibition of intrinsic 5-HT2B receptor cells. 5-HT2B receptor expression was identified in the megakaryocytic activity prevented TNAP activation. In contrast, agonist stimulation of cell lineage. Serotonin promoted the proliferation of megakaryocytes the receptor further increased TNAP activity during the initial minerali- (MKs) and reduced cell apoptosis via activation of the 5-HT2B receptor zation phase. Previous observations indicated that the 5-HT2B receptor and the Akt pathway (Liu & Fanburg, 2006). Serotonin increased L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36 29 proplatelet-bearing MKs and polymerized actin levels via ERK1/2 findings indicate that serotonin plays a fundamental role in arthritis (Ye et al., 2014). Mice deficient in peripheral 5-HT (Tph1−/−) displayed by regulating the Th17/T-regulatory cell balance and osteoclastogenesis morphological and cellular features of ineffective erythropoiesis. (Chabbi-Achengli et al., 2016).

The central event occurred in the bone marrow, where the absence of Therefore, 5-HT signalling via the 5-HT2A and 5-HT2B receptors 5-HT hampered the progression of erythroid precursors that express mediates the balance among various haematopoietic lineages.

5-HT2A and 5-HT2B receptors towards terminal differentiation. In addition, red blood cells from 5-HT-deﬁcient mice were more sensitive 4.2. Amyotrophic lateral sclerosis to macrophage phagocytosis and have a shortened in vivo half-life

(Amireault et al., 2011). Furthermore, 5-HT2B receptor expression was Amyotrophic lateral sclerosis (ALS) is the major adult onset motor detected in c-kit + bone marrow cells (Launay et al., 2012). The neuron disease and represents the third most frequent neurodegenera-

5-HT2B receptor antagonist RS127445 decreased colony-forming capac- tive disease after Alzheimer's disease and Parkinson's disease. ALS ity by inhibiting both CFU-GEMM and BFU-E formation; this results is characterized by the selective degeneration of upper motor neurons can be attributed to a reduction of cell proliferation and/or an apoptotic in the cerebral cortex and lower motor neurons in the spinal cord effect. By contrast, 5-HT significantly enhanced the expansion of and brainstem and leads to progressive paralysis and death within CD34+ cells to early stem/progenitors (CFU-GEMM) and committed 3–5 years after onset. Spinal cord injury leads to an initial phase of progenitors (BFU/CFU-E) (Yang et al., 2007). Treatment with aggregat- hyporeflexia followed by hyperreflexia, often referred to as spasticity. ed (1–40 or 1–42) and oligomeric (1–42) amyloid β (Aβ, a hallmark Spasticity is a common and disabling symptom observed in patients of Alzheimer's disease) promoted the differentiation of bone marrow- with ALS. A rat tail-spasticity model with a caudal spinal transection derived mesenchymal stem cells without toxic effects. The effect of Aβ identified that the expression of 5-HT2B receptors was downregulated was shown to be mediated by GPCRs, neuropeptide Y1 and the 5-HT2B at 21 days post-injury (Wienecke et al., 2010). Motoneurons, which receptor via PI3K-dependent activation of the MAPK/ERK1/2 pathway help recover from denervation, function autonomously by exhibiting (Kim et al., 2009). large persistent calcium currents that help with the functional recovery In human macrophages, 5-HT was reported to inhibit the and contribute to uncontrolled muscle spasms. Application of agonists lipopolysaccharide-induced release of proinflammatory cytokines, to to 5-HT2B receptors (including BW723C86) significantly increased upregulate the expression of M2 polarization-associated genes and these persistent calcium currents. 5-HT2B receptors on motoneurons to reduce the expression of M1-associated genes. The 5-HT2B receptor ultimately contribute to the recovery of motoneuron function and the mediates the pro-M2 skewing effect of 5-HT. In fact, blocking signalling emergence of spasms (Murray et al., 2011). In ALS, spasticity is tradi- through this receptor during in vitro monocyte-to-macrophage differ- tionally thought to be the result of degeneration of the upper motor entiation preferentially modulates the acquisition of M2 polarization neurons in the cerebral cortex, although the degeneration of other neu- markers. Htr2B mRNA was found to be preferentially expressed in anti- ronal types (serotonergic neurons in particular) might also represent a inflammatory M2 (M-CSF) macrophages and was detected in vivo in cause of spasticity. In SOD1 (G86R) mice, which are a transgenic both liver Kupffer cells and tumour-associated macrophages (de Las model of ALS, 5-HT levels were decreased in the brainstem and spinal

Casas-Engel et al., 2013). Recently, expression of the 5-HT2B receptor cord before the onset of motor symptoms. Furthermore, there was was reported on postnatal microglia, supporting the notion that 5-HT noticeable atrophy of 5-HT neuronal cell bodies along with neuritic participates in the temporal and spatial synchronization of microglial degeneration at the initial disease onset. In SOD1 (G86R) mice, function (Kolodziejczak et al., 2015). spastic-like contractions in the tail muscle were observed at the end-

Htr2B mRNA expression was found in the spleen, thymus, and stage. Importantly, these contractions were abolished by treatment peripheral blood lymphocytes (Stefulj et al., 2000). Study of the expres- with the 5-HT2B/2C receptors inverse agonist SB206553. In line with sion of serotonergic receptors in human dendritic cells showed that this result, 5-HT2B receptor expression was strongly increased at disease immature dendritic cells expressed Htr2B mRNA. Moreover, 5-HT2B re- onset (Dentel et al., 2013). 2+ ceptor stimulation induced intracellular Ca mobilization in immature In summary, 5-HT2B receptors in motoneurons may ultimately but not mature dendritic cells. Serotonin stimulated different signalling contribute to the recovery of motoneuron function and the emergence pathways in dendritic cells in a maturation-dependent manner (Idzko of spasms. et al., 2004). A proper balance between different T helper (Th) cell sub- Microglia are the resident mononuclear phagocytes of the central sets is necessary for normal functioning of the adaptive immune system. nervous system and have been implicated in the pathogenesis of In human umbilical cord blood, T helper cells cultured in the absence neurodegenerative diseases such as ALS. During neurodegeneration, and presence of cytokines promoting either Th1 or Th2 differentiation microglial activation is accompanied by infiltration of circulating mono- were found to specifically express HTR2B among 50 differentially cytes, leading to the production of multiple inflammatory mediators in expressed Th2 genes (Aijö et al., 2012). In gene expression profiles the spinal cord. Degenerative alterations in mononuclear phagocytes during human CD41 T cell differentiation, HTR2B was found to be SP4- are commonly observed during neurodegenerative diseases. In mutant specific (~10-fold) among the sixteen transcripts that were expressed SOD1 mice, 5-HT2B receptor upregulation was observed but was in SP4 thymocytes at levels 3-fold or higher; this level expression was restricted to cells positive for CD11b, a marker of mononuclear phago- greater than in any other isolated T cell subpopulation (Lee et al., 2004). cytes including microglia. Ablation of the 5-HT2B receptor in transgenic Rheumatoid arthritis is a chronic disease that results in a disabling ALS mice expressing mutant SOD1 resulted in increased degeneration and painful condition as it progresses to the destruction of the articular of mononuclear phagocytes, as evidenced by the fragmentation of cartilage and ankylosis of the joints. Although the cause of the disease Iba1-positive cellular processes, which was accompanied by not only is still unknown, evidence has argued that autoimmunity plays an decreased expression of key neuroinflammatory genes but also a loss important part. There are increasing views regarding 5-HT as being of the expression of homeostatic microglial genes. Importantly, the dra- associated with the activation of immunoinflammatory pathways and matic effect of 5-HT2B receptor ablation on mononuclear phagocytes the onset of autoimmune reactions. In Tph1−/− mice with arthritis, a was associated with the acceleration of disease progression (El Oussini significant increase in osteoclast differentiation and bone resorption et al., 2016). A study on polymorphisms in the human HTR2B gene was observed with an increase in IL-17 levels in the paws and in the (which encodes the 5-HT2B receptor) in a large cohort of ALS patients number of Th17 lymphocytes in the draining lymph nodes, whereas showed that the C allele of SNP rs10199752 in the HTR2B gene was asso- the number of T-regulatory cells was dampened. Ex vivo 5-HT and ciated with longer survival. Moreover, patients carrying one copy of the agonists at the 5-HT2A and 5-HT2B receptors restored IL-17 secretion C allele of SNP rs10199752 showed increased HTR2B mRNA expression from splenocytes and Th17 cell differentiation in Tph1−/− mice. These in the spinal cord and displayed less pronounced degeneration of 30 L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36

Iba1-positive cells than patients carrying two copies of the more com- human islets derived from non-diabetic and type 2 diabetic patients mon A allele (El Oussini et al., 2016). highlighted the overexpression of HTR1D and HTR2A mRNA in diabetic Thus, the 5-HT2B receptor limits the degeneration of spinal cord subjects. In fact, the effects of 5-HT in the pancreas are complex and mononuclear phagocytes (most likely microglia) and slows the disease could vary depending on the pathophysiological status. 5-HT was progression of ALS. found to inhibit insulin and glucagon secretion in islets from non- diabetic subjects whereas 5-HT increased insulin release in response 4.3. Obesity/metabolic syndrome to glucose in islets from type 2 diabetic patients (Bennet et al., 2015). Taken together, these results suggest that 5-HT regulates insulin se- The serotonergic system affects feeding behaviour not only at the cretion in non-diabetic islets; however, the stimulation of overexpressed central nervous system level but also at the peripheral level by regulat- 5-HT1D and 5-HT2A receptors contributes to islet dysfunction in type 2 ing glucose and lipid metabolism (McGlashon et al., 2015). A strong diabetic patients. lactogen-dependent upregulation of 5-HT biosynthesis has been On the other hand, gut-derived 5-HT favours lipolysis and liver shown to occur in a subpopulation of mouse islet β-cells during preg- neoglucogenesis and inhibits glucose uptake in liver and adipose nancy (Schraenen et al., 2010). This subpopulation of pancreatic islet tissue by signalling through the 5-HT2B receptor. Inhibition of peripheral cells expresses genes that encode all of the products necessary for 5-HT synthesis and blockade of 5-HT2B receptor signalling improves synthesizing, packaging, and secreting 5-HT, including tryptophan hyperglycaemia in a mouse model of type 2 diabetes (Sumara et al., hydroxylases. Transcriptome analysis of islets isolated from pregnant 2012). In a high-throughput RNA screen with human primary mice identified a very strong upregulation of two paralogous genes (pre)adipocytes, 110 genes were found to be regulated at the gene that encode tryptophan hydroxylase, Tph1 and Tph2 (Goyvaerts et al., expression level during adipogenesis. Among these, HTR2B mRNA was 2016); this upregulation is dependent on the activation of prolactin one of the top hits identified. Adipocytes cultured in the presence of receptors. In β-cells, Pet1 can bind to the serotonergic genes but also the 5-HT2B receptor-selective antagonist RS127445 exhibited a signifi- to a conserved insulin gene regulatory element. In Tph1−/− mice, the cant increase in neutral lipid levels compared to control cells (Söhle absence of 5-HT leads to impaired insulin secretion and, as a conse- et al., 2012). A recent study highlighted the role of peripheral 5-HT in quence, reduced glucose tolerance (Ohta et al., 2011). The mechanism brown adipose tissue thermogenesis. Tph1-deficient mice are protected could be impaired serotonylation of the small GTPases Rab3a and from obesity and insulin resistance by elevated brown adipose tissue Rab27a, which are two key players for insulin exocytosis (Paulmann activity. This mechanism implies inhibition of β-adrenergic signalling et al., 2009). Nevertheless, it remains debatable whether blocking by 5-HT (Crane et al., 2015). These studies suggest that peripheral 5-HT receptor signalling in pregnant mice also blocks β-cell expansion 5-HT regulates glucose and lipid metabolism, fat accumulation, and obe- and causes glucose intolerance (Goyvaerts et al., 2016; Kim et al., sity. The last major organ involved in glucose metabolism is the muscle. 2010). The differential expression of the 5-HT receptor genes in Recently, in mice fed a high-fat diet, Watanabe et al. (2016) observed a

Psychosis (negative Amyotrophic lateral Antiobesity (anorectic symptoms) sclerosis effect)

Osteopenia (Bone formation and cellular differenciation) 5-HT 5-HT 2A 5-HT2B 2C

-Cardiovascular risk Migraine -Chronic artery disease -Fibrosis (liver, skin, heart) -Cardiac hypertrophy - Hypertension Agonist -Pulmonary arterial Inverse agonist hypertension -Valvular heart Antagonist disease

Fig. 1. Serotonin 5-HT2 receptors as therapeutic targets for central nervous system and cardiovascular diseases. Blocking or stimulating 5-HT2 receptors could have clinical impact in many fields. In this figure, the main areas are emphasized. We also show which type of receptor should be blocked or stimulated. L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36 31 reduction of weight gain, hyperglycaemia, and insulin resistance after Assetta, B., Maginnis, M. S., Gracia Ahufinger, I., Haley, S. A., Gee, G. V., Nelson, C. D. S., ... Atwood, W. J. (2013). 5-HT2 receptors facilitate JC polyomavirus entry. J Virol 87, intraperitoneal injections of high doses of 5-HT (0.1 mg, 0.5 mg or 13490–13498. 1 mg twice a week). The research team simultaneously observed a Auclair, A. L., Cathala, A., Sarrazin, F., Depoortère, R., Piazza, P. V., Newman-Tancredi, A., & shift in the metabolic profile in the muscle fibre of the soleus muscle. Spampinato, U. (2010). The central serotonin 2B receptor: A new pharmacological target to modulate the mesoaccumbens dopaminergic pathway activity. JNeurochem 5-HT injections induced an increase the mRNA expression of PPAR coac- 114,1323–1332. tivator 1α in the soleus muscle, which was inhibited by antagonists Audia, J. E., Evrard, D. A., Murdoch, G. R., Droste, J. J., Nissen, J. S., Schenck, K. W., ... Cohen, M. L. (1996). Potent, selective tetrahydro-beta-carboline antagonists of the serotonin against either the 5-HT or 5-HT receptors. 2A 7 2B (5-HT2B) contractile receptor in the rat stomach fundus. J Med Chem 39, – These data suggest important roles for the 5-HT2A and 5-HT2B recep- 2773 2780. tors in controlling energy homeostasis. Ayme-Dietrich, E., Lawson, R., Gasser, B., Dallemand, R., Bischoff, N., & Monassier, L. (2012). Mitral bioprosthesis hypertrophic scaring and native aortic valve fibrosis during benfluorex therapy. Fundam Clin Pharmacol 26,215–218. Ayme-Dietrich, E., Marzak, H., Lawson, R., Mokni, W., Wendling, O., Combe, R., ... 5. Conclusions and prospects Monassier, L. (2015). Contribution of serotonin to cardiac remodeling associated with hypertensive diastolic ventricular dysfunction in rats. J Hypertens 33, – After many years of investigations in various fields such as fibrosis, 2310 2321. Bai, C. -F., Liu, J. -C., Zhao, R., Cao, W., Liu, S. -B., Zhang, X. -N., ... Zhao, M. -G. (2010). Role the central nervous system and the cardiovascular system, new para- of 5-HT2B receptor in cardiomyocyte apoptosis of norepinephrine-induced cardiomyopathy model in rats. Clin Exp Pharmacol Physiol 37,e145–e151. digms of the pathophysiological contributions of 5-HT2 receptors have fi fi Banas, S., Doly, S., Boutourlinsky, K., Diaz, S., Belmer, A., Callebert, J., ... Maroteaux, L. been discovered and clari ed. In parallel, pharmacochemistry identi ed (2011). Deconstructing antiobesity compound action: Requirement of serotonin new selective ligands and highlighted multiple 5-HT2 receptor intracel- 5-HT2B receptors for dexfenfluramine anorectic effects. Neuropsychopharmacology lular signalling pathways. At that step, translational research will be 36,423–433. Barre, A., Berthoux, C., De Bundel, D., Valjent, E., Bockaert, J., Marin, P., & Becamel, C. required to determine clinical applications. Nevertheless, the observed (2016). Presynaptic serotonin 2A receptors modulate thalamocortical plasticity and cardiovascular side effects have ignited the interest for agonists. With associative learning. Proc Natl Acad Sci U S A 113,E1382–E1391. regard to this obstacle, the search for allosteric modulators and biased Baudry, A., Bitard, J., Mouillet-Richard, S., Locker, M., Poliard, A., Launay, J. -M., & Kellermann, O. (2010). The serotonergic 5-HT2B receptor controls tissue non-specific alkaline ligands will be of great importance. On the other hand, the use of highly phosphatase activity in osteoblasts via eicosanoids and phosphatidylinositol-specific phospholipase C. JBiolChem285, 26066–26073. selective 5-HT2 receptor antagonists seems to be safe and could prevent Becamel, C., Figge, A., Poliak, S., Dumuis, A., Peles, E., Bockaert, J., ... Ullmer, C. (2001). and/or treat many diseases (Cf Fig. 1). Interaction of serotonin 5-HT2C receptors with PDZ10 of the multi PDZ protein MUPP1. J Biol Chem 276,12974–12982. Belmer, A., Doly, S., Setola, V., Banas, S. M., Moutkine, I., Boutourlinsky, K., ... Maroteaux, L. Conflict of interest (2014). Role of the N-terminal region in G-protein coupled receptor functions: Negative modulation revealed by 5-HT2B receptor polymorphisms. Mol Pharmacol – fl 85,127 138. The authors declare that there are no con icts of interest. Bennet, H., Balhuizen, A., Medina, A., Dekker Nitert, M., Ottosson Laakso, E., Essen, S., ... Fex, M. (2015). Altered serotonin (5-HT) 1D and 2A receptor expression may contribute to defective insulin and glucagon secretion in human type 2 diabetes. Peptides 71, Acknowledgments 113–120. Berg, K. A., Maayani, S., Goldfarb, J., Scaramellini, C., Leff, P., & Clarke, W. P. (1998). Effector pathway-dependent relative efficacy at serotonin type 2A and 2C receptors: Evidence LMa's work has been supported by funds from the Centre National for agonist-directed trafficking of receptor stimulus. Mol Pharmacol 54,94–104. de la Recherche Scientifique, the Institut National de la Santé et de la Berglund, E. D., Liu, C., Sohn, J. -W., Liu, T., Kim, M. H., Lee, C. E., ... Elmquist, J. K. (2013). Recherche Médicale, the Université Pierre et Marie Curie, and by grants Serotonin 2C receptors in pro-opiomelanocortin neurons regulate energy and glucose homeostasis. JClinInvest123,5061–5070. from the Fondation pour la Recherche sur le Cerveau, the Fondation Bevilacqua, L., Doly, S., Kaprio, J., Yuan, Q., Tikkanen, R., Paunio, T., ... Goldman, D. (2010). A fi de France, the Fondation pour la Recherche Médicale “Equipe FRM population-speci cHTR2B stop codon predisposes to severe impulsivity. Nature 468, ” 1061–1066. DEQ2014039529 , the French Ministry of Research (Agence Nationale Bhatnagar, A., Willins, D. L., Gray, J. A., Woods, J., Benovic, J. L., & Roth, B. L. (2001). The pour la Recherche ANR-12-BSV1-0015-01 and the Investissements dynamin-dependent, arrestin-independent internalization of 5-hydroxytryptamine d'Avenir programme ANR-11-IDEX-0004-02). LM's team is part of the 2A (5-HT2A) serotonin receptors reveals differential sorting of arrestins and 5-HT2A receptors during endocytosis. J Biol Chem 276, 8269–8277. École des Neurosciences de Paris Ile-de-France network and of the Bittel, D. C., Kibiryeva, N., Sell, S. M., Strong, T. V., & Butler, M. G. (2007). Whole genome Bio-Psy Labex and, as such, this work was supported by French state microarray analysis of gene expression in Prader–Willi syndrome. Am J Med Genet A – funds managed by the ANR within the Investissements d'Avenir 143,430 442. Blasco-Fontecilla, H., Baca-Garcia, E., & de Leon, J. (2010). Do atypical antipsychotic drugs programme under reference ANR-11-IDEX-0004-02. reduce the risk of ischemic heart disease and mortality? Possible role of 5-HT2A receptor blockade. Schizophr Res 119,160–163. Bliziotes, M. M., Eshleman, A. J., Zhang, X. W., & Wiren, K. M. (2001). Neurotransmitter References action in osteoblasts: Expression of a functional system for serotonin receptor activation and reuptake. Bone 29,477–486. Abdallah, L., Bonasera, S. J., Hopf, F. W., O'Dell, L., Giorgetti, M., Jongsma, M., ... Tecott, L. H. Bonhaus, D. W., Bach, C., DeSouza, A., Salazar, F. H. R., Matsuoka, B. D., Zuppan, P., ... Eglen, (2009). Impact of serotonin 2C receptor null mutation on physiology and behavior as- R. M. (1995). The pharmacology and distribution of human 5-hydroxytryptamine 2B sociated with nigrostriatal dopamine pathway function. J Neurosci 29,8156–8165. (5-HT2B) receptor gene products: Comparison with 5-HT2A and 5-HT2C receptors. Br J Aijö, T., Edelman, S. M., Lönnberg, T., Larjo, A., Kallionpää, H., Tuomela, S., ... Lähdesmäki, H. Pharmacol 115,622–628. (2012). An integrative computational systems biology approach identifies differen- Bonhaus, D. W., Flippin, L. A., Greenhouse, R. J., Jaime, S., Rocha, C., Dawson, M., ... Martin, fi tially regulated dynamic transcriptome signatures which drive the initiation of G. R. (1999). RS-127445: A selective, high af nity, orally bioavailable 5-HT2B receptor human T helper cell differentiation. BMC Genomics 13,572. antagonist. Br J Pharmacol 127,1075–1082. Albizu, L., Holloway, T., Gonzalez-Maeso, J., & Sealfon, S. C. (2011). Functional Bonhaus, D. W., Weinhardt, K. K., Taylor, M., DeSouza, A., McNeeley, P. M., Szczepanski, K., fi crosstalk and heteromerization of serotonin 5-HT2A and dopamine D2 receptors. ... Eglen, R. M. (1997). RS-102221: A novel high af nity and selective, 5-HT2C receptor Neuropharmacology 61,770–777. antagonist. Neuropharmacology 36,621–629. Amireault, P., Hatia, S., Bayard, E., Bernex, F., Collet, C., Callebert, J., ... Côté, F. (2011). Booth, R. G., Fang, L., Huang, Y., Wilczynski, A., & Sivendran, S. (2009). (1R, 3S)-(−)-trans- fi Ineffective erythropoiesis with reduced red blood cell survival in serotonin- PAT: A novel full-ef cacy serotonin 5-HT2C receptor agonist with 5-HT2A and 5-HT2B deficient mice. Proc Natl Acad Sci U S A 108,13141–13146. receptor inverse agonist/antagonist activity. Eur J Pharmacol 615,1–9. Anastasio, N. C., Stutz, S. J., Fink, L. H. L., Swinford-Jackson, S. E., Sears, R. M., DiLeone, R. J., Bourson, A., Wanner, D., Wyler, R., Petit, N., Zwingelstein, C., Rudler, A., & Sleight, A. J. ... Cunningham, K. A. (2015). Serotonin (5-HT) 5-HT2A receptor (5-HT2AR):5-HT2CR (1996). Pharmacologic evaluation of the discriminative stimulus of metachloro- imbalance in medial prefrontal cortex associates with motor impulsivity. ACS Chem phenylpiperazine. Pharmacol Biochem Behav 53,107–114. Neurosci 6, 1248–1258. Bracha, S., Viall, A., Goodall, C., Stang, B., Ruaux, C., Seguin, B., & Chappell, P. E. (2013). Antonini, A., & Poewe, W. (2007). Fibrotic heart-valve reactions to dopamine-agonist The expression and role of serotonin receptor 5HTR2A in canine osteoblasts and an treatment in Parkinson's disease. Lancet Neurol 6,826–829. osteosarcoma cell line. BMC Vet Res 9, 251. Arslan, A. A., Gold, L. I., Mittal, K., Suen, T. C., Belitskaya-Levy, I., Tang, M. S., & Toniolo, P. Branchek, T., Adham, N., Macchi, M., Kao, H. T., & Hartig, P. R. (1990). [3H]-DOB(4-bromo- (2005). Gene expression studies provide clues to the pathogenesis of uterine 2,5-dimethoxyphenylisopropylamine) and [3H] ketanserin label two affinity states of leiomyoma: New evidence and a systematic review. Hum Reprod 20,852–863. the cloned human 5-hydroxytryptamine2 receptor. Mol Pharmacol 38,604–609. Asada, M., Ebihara, S., Yamanda, S., Niu, K., Okazaki, T., Sora, I., & Arai, H. (2009). Depletion Brattelid, T., Tveit, K., Birkeland, J. A., Sjaastad, I., Qvigstad, E., Krobert, K. A., ... Levy, F. O. of serotonin and selective inhibition of 2B receptor suppressed tumor angiogenesis by (2007). Expression of mRNA encoding G protein-coupled receptors involved in con- inhibiting endothelial nitric oxide synthase and extracellular signal-regulated kinase gestive heart failure—A quantitative RT-PCR study and the question of normalisation. 1/2 phosphorylation. Neoplasia 11,408–417. Basic Res Cardiol 102,198–208. 32 L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36

Brea,J.,Castro,M.,Giraldo,J.,López-Giménez,J.F.,Padín,J.F.,Quintián,F.,...Loza, Depoortere, I., Thijs, T., & Peeters, T. (2006). The contractile effect of the ghrelin receptor M. I. (2009). Evidence for distinct antagonist-revealed functional states of 5- antagonist, D-Lys3-GHRP-6, in rat fundic strips is mediated through 5-HT receptors. hydroxytryptamine(2A) receptor homodimers. Mol Pharmacol 75,1380–1391. Eur J Pharmacol 537,160–165. Canal,C.E.,&Morgan,D.(2012).Head-twitch response in rodents induced by the Devroye, C., Cathala, A., Di Marco, B., Caraci, F., Drago, F., Piazza, P. V., & Spampinato, U. (2015). hallucinogen 2,5-dimethoxy-4-iodoamphetamine: A comprehensive history, a Central serotonin2B receptor blockade inhibits cocaine-induced hyperlocomotion re-evaluation of mechanisms, and its utility as a model. Drug Test Anal 4,556–576. independently of changes of subcortical dopamine outflow. Neuropharmacology 97, Canal, C. E., Morgan, D., Felsing, D., Kondabolu, K., Rowland, N. E., Robertson, K. L., ... Booth, 329–337. R. G. (2014). A novel aminotetralin-type serotonin (5-HT) 2C receptor-specificagonist Diaz, S. L., Doly, S., Narboux-Nême, N., Fernandez, S., Mazot, P., Banas, S., ... Maroteaux, L. and 5-HT2A competitive antagonist/5-HT2B inverse agonist with preclinical efficacy (2012). 5-HT2B receptors are required for serotonin-selective antidepressant actions. for psychoses. J Pharmacol Exp Ther 349,310–318. Mol Psychiatry 17,154–163. Canal, C. E., Olaghere da Silva, U. B., Gresch, P. J., Watt, E. E., Sanders-Bush, E., & Airey, D. C. Dimitrova-Nakov, S., Baudry, A., Harichane, Y., Collet, C., Marchadier, A., Kellermann, O., & (2010). The serotonin 2C receptor potently modulates the head-twitch response in Goldberg, M. (2014). Deletion of serotonin 2B receptor provokes structural alterations mice induced by a phenethylamine hallucinogen. Psychopharmacology 209,163–174. of mouse dental tissues. Calcif Tissue Int 94,293–300. Chabbi-Achengli, Y., Coman, T., Collet, C., Callebert, J., Corcelli, M., Lin, H., ... Côté, F. (2016). Ding, C., Bremer, N. M., Smith, T. D., Seitz, P. K., Anastasio, N. C., Cunningham, K. A., & Zhou, Serotonin is involved in autoimmune arthritis through Th17 immunity and bone J. (2012). Exploration of synthetic approaches and pharmacological evaluation of resorption. Am J Pathol 186,927–937. PNU-69176E and its stereoisomer as 5-HT2C receptor allosteric modulators. ACS Chabbi-Achengli, Y., Launay, J. -M., Maroteaux, L., De Vernejoul, M. C., & Collet, C. (2013). Chem Neurosci 3,538–545. Serotonin 2B receptor (5-HT2B R) signals through prostacyclin and PPAR-ß/δ in Dizeyi,N.,Bjartell,A.,Hedlund,P.,Tasken,K.A.,Gadaleanu,V.,&Abrahamsson,P.A. osteoblasts. PLoS One 8,e75783. (2005). Expression of serotonin receptors 2B and 4 in human prostate cancer Chan, S. Y., & Loscalzo, J. (2008). Pathogenic mechanisms of pulmonary arterial hyperten- tissue and effects of their antagonists on prostate cancer cell lines. Eur Urol 47, sion. J Mol Cell Cardiol 44,14–30. 895–900. Chanrion, B., Mannoury la Cour, C., Gavarini, S., Seimandi, M., Vincent, L., Pujol, J. F., ... Doly, S., Bertran-Gonzalez, J., Callebert, J., Bruneau, A., Banas, S. M., Belmer, A., ... Millan, M. J. (2008). Inverse agonist and neutral antagonist actions of antidepressants Maroteaux, L. (2009). Role of serotonin via 5-HT2B receptors in the reinforcing effects at recombinant and native 5-hydroxytryptamine2C receptors: Differential modulation of MDMA in mice. PLoS One 4, e7952. of cell surface expression and signal transduction. Mol Pharmacol 73,748–757. Doly, S., Valjent, E., Setola, V., Callebert, J., Herve, D., Launay, J. M., & Maroteaux, L. (2008). Chen, Y. X., Wang, W. D., Song, X. J., Gu, Y. Q., Tian, H. Y., Hu, H. J., ... Liu, C. W. (2015). Pro- Serotonin 5-HT2B receptors are required for 3,4-methylenedioxymethamphetamine- spective randomized study of sarpogrelate versus clopidogrel-based dual antiplatelet induced hyperlocomotion and 5-HT release in vivo and in vitro. JNeurosci28, therapies in patients undergoing femoropopliteal arterial endovascular interventions: 2933–2940. Preliminary results. Chin Med J 128,1563–1566. Dumitrascu, R., Kulcke, C., Königshoff, M., Kouri, F., Yang, X., Morrell, N., ... Pullamsetti, S. S. Chenu, F., Shim, S., El Mansari, M., & Blier, P. (2014). Role of melatonin, serotonin 2B,and (2011). Terguride ameliorates monocrotaline-induced pulmonary hypertension in serotonin 2C receptors in modulating the firing activity of rat dopamine neurons. rats. Eur Respir J 37,1104–1118. J Psychopharmacol (Oxf) 28,162–167. Ebrahimkhani, M., Oakley, F., Murphy, L., Mann, J., Moles, A., Perugorria, M., ... Mann, D. Choi, D. -S., Birraux, G., Launay, J. -M., & Maroteaux, L. (1994). The human serotonin (2011). Stimulating healthy tissue regeneration by targeting the 5-HT2B receptor in 5-HT2B receptor: Pharmacological link between 5-HT2 and 5-HT1D receptors. FEBS chronic liver disease. Nat Med 17, 1668–1673. Lett 352,393–399. El Oussini, H., Bayer, H., Scekic-Zahirovic, J., Vercruysse, P., Sinniger, J., Dirrig-Grosch, S., ... Christopoulos, A., & Kenakin, T. (2002). G protein-coupled receptor allosterism and Dupuis, L. (2016). Serotonin 2B receptor slows disease progression and prevents de- complexing. Pharmacol Rev 54,323–374. generation of spinal cord mononuclear phagocytes in amyotrophic lateral sclerosis. Clifton, P. G., Lee, M. D., & Dourish, C. T. (2000). Similarities in the action of Ro 60-0175, Acta Neuropathol. a5-HT2C receptor agonist and d-fenfluramine on feeding patterns in the rat. Elphick, G. F., Querbes, W., Jordan, J. A., Gee, G. V., Eash, S., Manley, K., ... Atwood, W. J. Psychopharmacology 152,256–267. (2004). The human polyomavirus, JCV, uses serotonin receptors to infect cells. Cohen, M. L., Schenck, K. W., Mabry, T. E., Nelson, D. L., & Audia, J. E. (1996). Science 306,1380–1383. LY272015, a potent, selective and orally active 5-HT2B receptor antagonist. JSer Fabre, A., Marchal-Sommé, J., Marchand-Adam, S., Quesnel, C., Borie, R., Dehoux, M., ... Res 3,131–144. Crestani, B. (2008). Modulation of bleomycin-induced lung fibrosis by serotonin Collet, C., Schiltz, C., Geoffroy, V., Maroteaux, L., Launay, J. -M., & de Vernejoul, M. -C. receptor antagonists in mice. Eur Respir J 32,426–436. (2008). The serotonin 5-HT2B receptor controls bone mass via osteoblast recruitment Fantegrossi, W. E., Simoneau, J., Cohen, M. S., Zimmerman, S. M., Henson, C. M., Rice, K. C., and proliferation. FASEB J 22,418–427. & Woods, J. H. (2010). Interaction of 5-HT2A and 5-HT2C receptors in R(−)-2,5- Conductier, G., Crosson, C., Hen, R., Bockaert, J., & Compan, V. (2005). 3,4-N- dimethoxy-4-iodoamphetamine-elicited head twitch behavior in mice. J Pharmacol methlenedioxymethamphetamine-induced hypophagia is maintained in 5-HT1B Exp Ther 335,728–734. receptor knockout mice, but suppressed by the 5-HT2C receptor antagonist Fernandez-Ranvier, G. G., Weng, J., Yeh, R. F., Khanafshar, E., Suh, I., Barker, C., ... Kebebew, RS102221. Neuropsychopharmacology 30,1056–1063. E. (2008). Identification of biomarkers of adrenocortical carcinoma using Connolly, H. M., Crary, J. L., McGoon, M. D., Hensrud, D. D., Edwards, B. S., Edwards, W. D., genomewide gene expression profiling. Arch Surg 143,841–846. & Schaff, H. V. (1997). Valvular heart disease associated with fenfluramine- Fitzgerald, L. W., Burn, T. C., Brown, B. S., Patterson, J. P., Corjay, M. H., Valentine, P. A., ... phentermine. N Engl J Med 337,581–588. Robertson, D. W. (2000). Possible role of valvular serotonin 5-HT2B receptors in the Corominas, R., Sobrido, M. J., Ribasés, M., Cuenca-León, E., Blanco-Arias, P., cardiopathy associated with fenfluramine. Mol Pharmacol 57,75–81. Narberhaus, B., ... Cormand, B. (2010). Association study of the serotoninergic Foguet, M., Hoyer, D., Pardo, L. A., Parekh, A., Kluxen, F. W., Kalkman, H. O., ... Lübbert, H. system in migraine in the Spanish population. Am J Med Genet B Neuropsychiatr (1992a). Cloning and functional characterization of the rat stomach fundus serotonin Genet 153B, 177–184. receptor. EMBO J 11,3481–3487. Crane, J. D., Palanivel, R., Mottillo, E. P., Bujak, A. L., Wang, H., Ford, R. J., ... Steinberg, G. R. Foguet, M., Nguyen, H., Le, H., & Lübbert, H. (1992b). Structure of the mouse 5-HT1C, (2015). Inhibiting peripheral serotonin synthesis reduces obesity and metabolic dys- 5-HT2 and stomach fundus serotonin receptor genes. Neuroreport 3,345–348. function by promoting brown adipose tissue thermogenesis. Nat Med 21,166–172. Fribourg, M., Moreno, J. L., Holloway, T., Provasi, D., Baki, L., Mahajan, R., ... Logothetis, D. E. Cremer, S. E., Moesgaard, S. G., Rasmussen, C. E., Zois, N. E., Falk, T., Reimann, M. J., ... Olsen, (2011). Decoding the signaling of a GPCR heteromeric complex reveals a unifying L. H. (2015b). Alpha-smooth muscle actin and serotonin receptors 2A and 2B in dogs mechanism of action of antipsychotic drugs. Cell 147,1011–1023. with myxomatous mitral valve disease. Res Vet Sci 100,197–206. Fujita, M., Minamino, T., Sanada, S., Asanuma, H., Hirata, A., Ogita, H., ... Kitakaze, M. Cremer, S. E., Zois, N. E., Moesgaard, S. G., Ravn, N., Cirera, S., Honge, J. L., ... Olsen, L. H. (2004). Selective blockade of serotonin 5-HT2A receptor increases coronary blood (2015a). Serotonin markers show altered transcription levels in an experimental flow via augmented cardiac nitric oxide release through 5-HT1B receptor in pig model of mitral regurgitation. Vet J 203,192–198. hypoperfused canine hearts. J Mol Cell Cardiol 37,1219–1223. Cunningham, K. A., Anastasio, N. C., Fox, R. G., Stutz, S. J., Bubar, M. J., Swinford, S. E., ... Garattini, S., Mennini, T., Bendotti, C., Invernizzi, R., & Samanin, R. (1986). Neurochemical Moeller, F. G. (2013). Synergism between a serotonin 5-HT2A receptor (5-HT2AR) mechanism of action of drugs which modify feeding via the serotoninergic system. antagonist and 5-HT2CR agonist suggests new pharmacotherapeutics for cocaine Appetite(7 Suppl), 15–38. addiction. ACS Chem Neurosci 4,110–121. Garcia-Pedraza, J. A., Garcia, M., Martin, M. L., San Roman, L., & Moran, A. (2014). Cussac, D., Boutet-Robinet, E., Ailhaud, M. C., Newman-Tancredi, A., Martel, J. C., Danty, N., The role of endothelium-derived hyperpolarizing factor and cyclooxygenase & Rauly-Lestienne, I. (2008). Agonist-directed trafficking of signalling at serotonin pathways in the inhibitory serotonergic response to the pressor effect elicited 5-HT2A, 5-HT2B and 5-HT2C-VSV receptors mediated Gq/11 activation and calcium by sympathetic stimulation in chronic sarpogrelate treated rats. Eur J Pharmacol mobilisation in CHO cells. Eur J Pharmacol 594,32–38. 731,80–87. Cussac, D., Newman-Tancredi, A., Quentric, Y., Carpentier, N., Poissonnet, G., Garfield, A. S., & Heisler, L. K. (2009). Pharmacological targeting of the serotonergic Parmentier, J. G., ... Millan, M. J. (2002). Characterization of phospholipase C activity system for the treatment of obesity. J Physiol 587,49–60. at h5-HT2C compared with h5-HT2B receptors: Influence of novel ligands upon Gavarini, S., Becamel, C., Altier, C., Lory, P., Poncet, J., Wijnholds, J., ... Marin, P. (2006). Op- membrane-bound levels of [3H]phosphatidylinositols. Naunyn Schmiedeberg's Arch posite effects of PSD-95 and MPP3 PDZ proteins on serotonin 5-hydroxytryptamine2C Pharmacol 365,242–252. receptor desensitization and membrane stability. Mol Biol Cell 17,4619–4631. de Las Casas-Engel, M., Domínguez-Soto, A., Sierra-Filardi, E., Bragado, R., Nieto, C., Puig- Gonzalez-Maeso, J., Ang, R. L., Yuen, T., Chan, P., Weisstaub, N. V., Lopez-Gimenez, J. F., ... Kroger, A., ... Corbí, A. L. (2013). Serotonin skews human macrophage polarization Sealfon, S. C. (2008). Identification of a serotonin/glutamate receptor complex impli- through HTR2B and HTR7. J Immunol 190,2301–2310. cated in psychosis. Nature 452,93–97. De Vry, J., & Schreiber, R. (2000). Effects of selected serotonin 5-HT(1) and 5-HT(2) receptor Goodall, E. M., Cowen, P. J., Franklin, M., & Silverstone, T. (1993). Ritanserin attenuates agonists on feeding behavior: Possible mechanisms of action. Neurosci Biobehav Rev 24, anorectic, endocrine and thermic responses to d-fenfluramine in human volunteers. 341–353. Psychopharmacology 112,461–466. Dees, C., Akhmetshina, A., Reich, N., Jüngel, A., Beyer, C., Krönke, G., ... Distler, J. H. W. Goyvaerts, L., Schraenen, A., & Schuit, F. (2016). Serotonin competence of mouse beta cells (2011). Platelet derived serotonin links vascular disease and tissue fibrosis. JExp during pregnancy. Diabetologia. Med 208,961–972. Halberstadt, A. L. (2015). Recent advances in the neuropsychopharmacology of serotonergic Dentel, C., Palamiuc, L., Henriques, A., Lannes, B., Spreux-Varoquaux, O., Gutknecht, L., ... hallucinogens. Behav Brain Res 277,99–120. Dupuis, L. (2013). Degeneration of serotonergic neurons in amyotrophic lateral Han, D. D., & Gu, H. H. (2006). Comparison of the monoamine transporters from human sclerosis: A link to spasticity. Brain 136,483–493. and mouse in their sensitivities to psychostimulant drugs. BMC Pharmacol 6,6. L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36 33

Hayashi, T., Sumi, D., Matsui-Hirai, H., Fukatsu, A., Arockia Rani, P. J., Kano, H., ... Iguchi, A. Kennett, G. A., Wood, M. D., Bright, F., Cilia, J., Piper, D. C., Gager, T., ... Blackburn, T. P. (2003). Sarpogrelate HCl, a selective 5-HT2A antagonist, retards the progression of (1996). In vitro and in vivo profile of SB 206553, a potent 5-HT2C/5-HT2B receptor atherosclerosis through a novel mechanism. Atherosclerosis 168,23–31. antagonist with anxiolytic-like properties. Br J Pharmacol 117,427–434. Heisler, L. K., Jobst, E. E., Sutton, G. M., Zhou, L., Borok, E., Thornton-Jones, Z., ... Cowley, M. Kim, S. W., Shin, I. S., Kim, J. M., Youn, T., Yang, S. J., Hwang, M. Y., & Yoon, J. S. (2009). A. (2006). Serotonin reciprocally regulates melanocortin neurons to modulate food The 5-HT2 receptor profiles of antipsychotics in the pathogenesis of obsessive– intake. Neuron 51,239–249. compulsive symptoms in schizophrenia. Clin Neuropharmacol 32,224–226. Heisler, L. K., Pronchuk, N., Nonogaki, K., Zhou, L., Raber, J., Tung, L., ... Tecott, L. H. (2007). Kim, H., Toyofuku, Y., Lynn, F. C., Chak, E., Uchida, T., Mizukami, H., ... German, M. S. Serotonin activates the hypothalamic–pituitary–adrenal axis via serotonin 2C recep- (2010). Serotonin regulates pancreatic beta cell mass during pregnancy. Nat Med tor stimulation. JNeurosci27,6956–6964. 16,804–808. Hendrikx, M., Van Dorpe, J., Flameng, W., & Daenen, W. (1996). Aortic and mitral valve Kishore, S., & Stamm, S. (2006). The snoRNA HBII-52 regulates alternative splicing of the disease induced by ergotamine therapy for migraine: A case report and review of serotonin receptor 2C. Science 311,230–232. the literature. J Heart Valve Dis 5,235–237. Kiss, B., Horváth, A., Némethy, Z., Schmidt, E., Laszlovszky, I., Bugovics, G., ... Szombathelyi, Herrick-Davis, K., Grinde, E., Harrigan, T. J., & Mazurkiewicz, J. E. (2005). Inhibition of Z. (2010). Cariprazine (RGH-188), a dopamine D(3) receptor-preferring, D(3)/ serotonin 5-hydroxytryptamine2C receptor function through heterodimerization: D(2) dopamine receptor antagonist-partial agonist antipsychotic candidate: In vitro Receptor dimers bind two molecules of ligand and one G-protein. J Biol Chem 280, and neurochemical profile. J Pharmacol Exp Ther 333,328–340. 40144–40151. Klein, D., Demory, A., Peyre, F., Kroll, J., Géraud, C., Ohnesorge, N., ... Goerdt, S. (2009). Herrick-Davis, K., Grinde, E., & Mazurkiewicz, J. E. (2004). Biochemical and biophysical Wnt2 acts as an angiogenic growth factor for non-sinusoidal endothelial cells and characterization of serotonin 5-HT2C receptor homodimers on the plasma membrane inhibits expression of stanniocalcin-1. Angiogenesis 12,251–265. of living cells. Biochemistry 43,13963–13971. Knight, A. R., Misra, A., Quirk, K., Benwell, K., Revell, D., Kennett, G., & Bickerdike, M. Hirai, T., Kaneshige, K., Kurosaki, T., & Nishio, H. (2010). Functional expression of 5-HT2A (2004). Pharmacological characterisation of the agonist radioligand binding site of receptor in osteoblastic MC3T3-E1 cells. Biochem Biophys Res Commun 396,278–282. 5-HT2A, 5-HT2B and 5-HT2C receptors. Naunyn Schmiedeberg's Arch Pharmacol 370, Hirai,T.,Tokumo,K.,Tsuchiya,D.,&Nishio,H.(2009).Expression of mRNA for 5-HT2 re- 114–123. ceptors and proteins related to inactivation of 5-HT in mouse osteoblasts. J Pharmacol Kodama, A., Komori, K., Hattori, K., Yamanouchi, D., Kajikuri, J., & Itoh, T. (2009). Sci 109,319–323. Sarpogrelate hydrochloride reduced intimal hyperplasia in experimental rabbit vein Hisaoka, K., Nishida, A., Takebayashi, M., Koda, T., Yamawaki, S., & Nakata, Y. (2004). graft. J Vasc Surg 49,1272–1281. Serotonin increases glial cell line-derived neurotrophic factor release in rat C6 glio- Kokubu, N., Tsuchihashi, K., Yuda, S., Hase, M., Eguchi, M., Wakabayashi, T., ... Shimamoto, blastoma cells. Brain Res 1002,167–170. K. (2006). Persistent insulin-sensitizing effects of sarpogrelate hydrochloride, a Hodge, J. M., Wang, Y., Berk, M., Collier, F. M., Fernandes, T. J., Constable, M. J., ... Williams, serotonin 2A receptor antagonist, in patients with peripheral arterial disease. Circ J L. J. (2013). Selective serotonin reuptake inhibitors inhibit human osteoclast and 70,1451–1456. osteoblast formation and function. Biol Psychiatry 74,32–39. Kolodziejczak, M., Bechade, C., Gervasi, N., Irinopoulou, T., Banas, S. M., Cordier, C., ... Horvath, J., Fross, R. D., Kleiner-Fisman, G., Lerch, R., Stalder, H., Liaudat, S., ... Lang, A. E. Maroteaux, L. (2015). Serotonin modulates developmental microglia via 5-HT2B (2004). Severe multivalvular heart disease: A new complication of the ergot deriva- receptors: Potential implication during synaptic refinement of retinogeniculate tive dopamine agonists. Mov Disord 19,656–662. projections. ACS Chem Neurosci 6,1219–1230. Hossain, M., Muntasir, H. A., Ishiguro, M., Bhuiyan, M. A., Rashid, M., Sugihara, T., & Königshoff, M., Dumitrascu, R., Udalov, S., Amarie, O. V., Reiter, R., Grimminger, F., ... Nagatomo, T. (2012). Mechanism of inverse agonist action of sarpogrelate at the con- Eickelberg, O. (2010). Increased expression of 5-hydroxytryptamine2A/B receptors stitutively active mutant of human 5-HT2A receptor revealed by molecular modeling. in idiopathic pulmonary fibrosis: A rationale for therapeutic intervention. Thorax Biol Pharm Bull 35, 1553–1559. 65,949–955. Idzko, M., Panther, E., Stratz, C., Müller, T., Bayer, H., Zissel, G., ... Ferrari, D. (2004). The Kopparapu, P. K., Tinzl, M., Anagnostaki, L., Persson, J. L., & Dizeyi, N. (2013). Expression serotoninergic receptors of human dendritic cells: Identification and coupling to and localization of serotonin receptors in human breast cancer. Anticancer Res 33, cytokine release. J Immunol 172,6011–6019. 363–370. Iizuka, K., Hamaue, N., Machida, T., Hirafuji, M., & Tsuji, M. (2009). Beneficial effects Kursar, J. D., Nelson, D. L., Wainscott, D., & Baez, M. (1994). Molecular cloning, functional of sarpogrelate hydrochloride, a 5-HT2A receptor antagonist, supplemented with expression, and mRNA tissue distribution of the human 5-hydroxytryptamine2B pioglitazone on diabetic model mice. Endocr Res 34,18–30. receptor. Mol Pharmacol 46,227–234. Iizuka, N., Oka, M., Yamada-Okabe, H., Hamada, K., Nakayama, H., Mori, N., ... Hamamoto, Kursar, J. D., Nelson, D. L., Wainscott, D. B., Cohen, M. L., & Baez, M. (1992). Molecular clon- Y. (2004). Molecular signature in three types of hepatocellular carcinoma with differ- ing, functional expression, and pharmacological characterisation of a novel serotonin ent viral origin by oligonucleotide microarray. Int J Oncol 24,565–574. (5-Hydroxytryptamine2F) from rat stomach fundus. Mol Pharmacol 42,549–557. Iwabayashi, M., Taniyama, Y., Sanada, F., Azuma, J., Iekushi, K., Kusunoki, H., ... Morishita, R. Labasque, M., Reiter, E., Becamel, C., Bockaert, J., & Marin, P. (2008). Physical interaction of (2012). Role of serotonin in angiogenesis: Induction of angiogenesis by sarpogrelate calmodulin with the 5-hydroxytryptamine2C receptor C-terminus is essential for G via endothelial 5-HT1B/Akt/eNOS pathway in diabetic mice. Atherosclerosis 220, protein-independent, arrestin-dependent receptor signaling. MolBiolCell19, 337–342. 4640–4650. Jaffre, F., Bonnin, P., Callebert, J., Debbabi, H., Setola, V., Doly, S., ... Maroteaux, L. (2009). Lairez, O., Cognet, T., Schaak, S., Calise, D., Guilbeau-Frugier, C., Parini, A., & Mialet-Perez, J. Serotonin and angiotensin receptors in cardiac fibroblasts coregulate adrenergic- (2013). Role of serotonin 5-HT2A receptors in the development of cardiac hypertro- dependent cardiac hypertrophy. Circ Res 104,113–123. phy in response to aortic constriction in mice. J Neural Transm (Vienna) 120,927–935. Jaffré, F., Callebert, J., Sarre, A., Etienne, N., Nebigil, C. G., Launay, J. M., ... Monassier, L. Lam, D. D., Przydzial, M. J., Ridley, S. H., Yeo, G. S., Rochford, J. J., O'Rahilly, S., & Heisler, L. K. (2004). Involvement of the serotonin 5-HT2B receptor in cardiac hypertrophy linked (2008). Serotonin 5-HT2C receptor agonist promotes hypophagia via downstream to sympathetic stimulation: Control of interleukin-6, interleukin-1 beta, and tumor activation of melanocortin 4 receptors. Endocrinology 149,1323–1328. necrosis factor-alpha cytokine production by ventricular fibroblasts. Circulation 110, Lampron, A., Bourdeau, I., Hamet, P., Tremblay, J., & Lacroix, A. (2006). Whole genome 969–974. expression profiling of glucose-dependent insulinotropic peptide (GIP)- and Janoshazi, A., Deraet, M., Callebert, J., Setola, V., Guenther, S., Saubamea, B., ... Maroteaux, L. adrenocorticotropin-dependent adrenal hyperplasias reveals novel targets for the (2007). Modified receptor internalization upon co-expression of 5-HT1B receptor study of GIP-dependent Cushing's syndrome. J Clin Endocrinol Metab 91,3611–3618. and 5-HT2B receptors. Mol Pharmacol 71,1463–1474. Lanteri, C., Doucet, E. L., Hernández Vallejo, S. J., Godeheu, G., Bobadilla, A. -C., Salomon, L., Jean, A., Conductier, G., Manrique, C., Bouras, C., Berta, P., Hen, R., ... Compan, V. (2007). ... Tassin, J. -P. (2014). Repeated exposure to MDMA triggers long-term plasticity of Anorexia induced by activation of serotonin 5-HT4 receptors is mediated by increases noradrenergic and serotonergic neurons. Mol Psychiatry 19,823–833. in CART in the nucleus accumbens. Proc Natl Acad Sci U S A 104,16335–16340. Launay, J. -M., Birraux, G., Bondoux, D., Callebert, J., Choi, D. -S., Loric, S., & Maroteaux, L. Jerman,J.C.,Brough,S.J.,Gager,T.,Wood,M.,Coldwell,M.C.,Smart,D.,&Middlemiss, (1996). Ras involvement in signal transduction by the serotonin 5-HT2B receptor. D. N. (2001). Pharmacological characterisation of human 5-HT2 receptor sub- J Biol Chem 271,3141–3147. types. Eur J Pharmacol 414,23–30. Launay, J. -M., Hervé, P., Callebert, J., Mallat, Z., Collet, C., Doly, S., ... Maroteaux, L. (2012). Ji, S. -P., Zhang, Y., Van Cleemput, J., Jiang, W., Liao, M., Li, L., ... Zhang, X. (2006). Disruption Serotonin 5-HT2B receptors are required for bone-marrow contribution to pulmonary of PTEN coupling with 5-HT2C receptors suppresses behavioral responses induced by arterial hypertension. Blood 119,1772–1780. drugs of abuse. Nat Med 12,324–329. Launay, J. M., Hervé, P., Peoc'h, K., Tournois, C., Callebert, J., Nebigil, C., ... Maroteaux, L. Johnson, K. W., Nelson, D. L., Dieckman, D. K., Wainscott, D. B., Lucaites, V. L., Audia, J. E., ... (2002). Function of the serotonin 5-hydroxytryptamine 2B receptor in pulmonary Phebus, L. A. (2003). Neurogenic dural protein extravasation induced by meta- hypertension. Nat Med 8,1129–1135. chlorophenylpiperazine (mCPP) involves nitric oxide and 5-HT2B receptor activation. Launay, J. M., Schneider, B., Loric, S., Da Prada, M., & Kellermann, O. (2006). Serotonin Cephalalgia 23,117–123. transport and serotonin transporter-mediated antidepressant recognition are Julius, D., MacDermott, A. B., Axel, R., & Jessell, T. M. (1988). Molecular characteri- controlled by 5-HT2B receptor signaling in serotonergic neuronal cells. FASEB J 20, zation of a functional cDNA encoding the serotonin 1c receptor. Science 241, 1843–1854. 558–564. Lee, M. S., Hanspers, K., Barker, C. S., Korn, A. P., & McCune, J. M. (2004). Gene expression Kamal, M., Gbahou, F., Guillaume, J. L., Daulat, A. M., Benleulmi-Chaachoua, A., Luka, M., ... profiles during human CD4+ T cell differentiation. Int Immunol 16, 1109–1124. Jockers, R. (2015). Convergence of melatonin and serotonin (5-HT) signaling at MT2/ Leibowitz, S. F., & Alexander, J. T. (1998). Hypothalamic serotonin in control of eating 5-HT2C receptor heteromers. J Biol Chem 290,11537–11546. behavior, meal size, and body weight. Biol Psychiatry 44,851–864. Kapetanaki, M. G., Mora, A. L., & Rojas, M. (2013). Influence of age on wound healing and Li, T., Weng, S. -G., Leng, X. -S., Peng, J. -R., Wei, Y. -H., Mou, D. -C., & Wang, W. -X. (2006). fibrosis. JPathol229,310–322. Effects of 5-hydroxytamine and its antagonists on hepatic stellate cells. HBPD INT 5, Kawamura, M., Ishiguro, M., Nagamine, T., & Houkin, K. (2013). Sarpogrelate dilates 96–100. cerebral arteries in the absence of exogenous serotonin. Neurol Med Chir (Tokyo) Liang, C., Chen, W., Zhi, X., Ma, T., Xia, X., Liu, H., ... Liang, T. (2013). Serotonin promotes 53,291–298. the proliferation of serum-deprived hepatocellular carcinoma cells via upregulation Kenakin, T., Watson, C., Muniz-Medina, V., Christopoulos, A., & Novick, S. (2012). A simple of FOXO3a. Mol Cancer 12,14. method for quantifying functional selectivity and agonist bias. ACS Chem Neurosci 3, Liang, Y. J., Lai, L. P., Wang, B. W., Juang, S. J., Chang, C. M., Leu, J. G., & Shyu, K. G. (2006). 193–203. Mechanical stress enhances serotonin 2B receptor modulating brain natriuretic pep- Kennett, G. A., Ainsworth, K., Trail, B., & Blackburn, T. P. (1997). BW 723C86, a 5-HT2B re- tide through nuclear factor-kappaB in cardiomyocytes. Cardiovasc Res 72,303–312. ceptor agonist, causes hyperphagia and reduced grooming in rats. Neuropharmacology Liu, Y., & Fanburg, B. L. (2006). Serotonin-induced growth of pulmonary artery smooth 36,233–239. muscle requires activation of PI3K/Akt/S6K1. Am J Respir Cell Mol Biol 34,182–191. 34 L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36

Liu, W., Wacker, D., Gati, C., Han, G. W., James, D., Wang, D., ... Cherezov, V. (2013). Nebigil, C. G., Launay, J. -M., Hickel, P., Tournois, C., & Maroteaux, L. (2000). 5- Serial femtosecond crystallography of G protein-coupled receptors. Science 342, Hydroxytryptamine 2B receptor regulates cell-cycle progression: Cross talk with tyro- 1521–1524. sine kinase pathways. Proc Natl Acad Sci U S A 97,2591–2596. Locker, M., Bitard, J., Collet, C., Poliard, A., Mutel, V., Launay, J. M., & Kellermann, O. (2006). Neill, J. C., & Cooper, S. J. (1989). Evidence that d-fenfluramine anorexia is mediated by Stepwise control of osteogenic differentiation by 5-HT2B receptor signaling: Nitric 5-HT1 receptors. Psychopharmacology 97,213–218. oxide production and phospholipase A2 activation. Cell Signal 18,628–639. Nelson, D. L., Lucaites, V. L., Wainscott, D. B., & Glennon, R. A. (1999). Comparisons of Loric, S., Launay, J. -M., Colas, J. -F., & Maroteaux, L. (1992). New mouse 5-HT2-like receptor: hallucinogenic phenylisopropylamine binding affinities at cloned human 5-HT2A, Expression in brain, heart, and intestine. FEBS Lett 312, 203–207. 5-HT2B and 5-HT2C receptors. Naunyn Schmiedeberg's Arch Pharmacol 359,1–6. Machida, T., Ohta, M., Onoguchi, A., Iizuka, K., Sakai, M., Minami, M., & Hirafuji, M. (2011). Nocito, A., Dahm, F., Jochum, W., Jang, J. H., Georgiev, P., Bader, M., ... Clavien, P. A. (2008). 5-Hydroxytryptamine induces cyclooxygenase-2 in rat vascular smooth muscle cells: Serotonin regulates macrophage-mediated angiogenesis in a mouse model of colon Mechanisms involving Src, PKC and MAPK activation [corrected]. Eur J Pharmacol 656, cancer allografts. Cancer Res 68, 5152–5158. 19–26. Nonogaki, K., Nozue, K., Takahashi, Y., Yamashita, N., Hiraoka, S., Kumano, H., ... Oka, Y. Magee, J. A., Araki, T., Patil, S., Ehrig, T., True, L., Humphrey, P. A., ... Milbrandt, J. (2001). (2007). Fluvoxamine, a selective serotonin reuptake inhibitor, and 5-HT2C receptor Expression profiling reveals hepsin overexpression in prostate cancer. Cancer Res inactivation induce appetite-suppressing effects in mice via 5-HT1B receptors. Int J 61,5692–5696. Neuropsychopharmacol 10,675–681. Mancia, F., Assur, Z., Herman, A. G., Siegel, R., & Hendrickson, W. A. (2008). Ligand Ohta, Y., Kosaka, Y., Kishimoto, N., Wang, J., Smith, S. B., Honig, G., ... German, M. S. (2011). sensitivity in dimeric associations of the serotonin 5HT2C receptor. EMBO Rep 9, Convergence of the insulin and serotonin programs in the pancreatic β-cell. Diabetes 363–369. 60,3208–3216. Manivet, P., Mouillet-Richard, S., Callebert, J., Nebigil, C. G., Maroteaux, L., Hosoda, S., ... Ohyashiki, J. H., Hamamura, R., Kobayashi,C.,Zhang,Y.,&Ohyashiki,K.(2008).Anet- Launay, J. -M. (2000). PDZ-dependent activation of nitric-oxide synthases by the work biology approach evaluating the anticancer effects of bortezomib identifies serotonin 2B receptor. J Biol Chem 275,9324–9331. SPARC as a therapeutic target in adult T-cell leukemia cells. AdvApplBioinform Mann, D. A., & Oakley, F. (2013). Serotonin paracrine signaling in tissue fibrosis. Biochim Chem 1,85–98. Biophys Acta 1832,905–910. Onken, M. D., Worley, L. A., Tuscan, M. D., & Harbour, J. W. (2010). An accurate, clinically Marion, S., Weiner, D. M., & Caron, M. G. (2004). RNA editing induces variation in desen- feasible multi-gene expression assay for predicting metastasis in uveal melanoma. sitization and trafficking of 5-hydroxytryptamine 2C receptor isoforms. J Biol Chem J Mol Diagn 12,461–468. 279, 2945–2954. Orejarena, M. J., Lanfumey, L., Maldonado, R., & Robledo, P. (2011). Involvement of 5-HT2A Martin, C. B. P., Hamon, M., Lanfumey, L., & Mongeau, R. (2014). Controversies on the role receptors in MDMA reinforcement and cue-induced reinstatement of MDMA-seeking of 5-HT(2C) receptors in the mechanisms of action of antidepressant drugs. Neurosci behaviour. Int J Neuropsychopharmacol 14,927–940. Biobehav Rev 42,208–223. Orton, E. C., Lacerda, C. M. R., & MacLea, H. B. (2012). Signaling pathways in mitral valve Martí-Solano, M., Sanz, F., Pastor, M., & Selent, J. (2014). A dynamic view of molecular degeneration. J Vet Cardiol 14,7–17. switch behavior at serotonin receptors: Implications for functional selectivity. PLoS Oufkir, T., Arseneault, M., Sanderson, J. T., & Vaillancourt, C. (2010). The 5-HT 2A serotonin One 9, e109312. receptor enhances cell viability, affects cell cycle progression and activates MEK- Marzak, H., Ayme-Dietrich, E., Lawson, R., Mokni, W., Combe, R., Becker, J., ... Monassier, L. ERK1/2 and JAK2-STAT3 signalling pathways in human choriocarcinoma cell lines. (2014). Old spontaneously hypertensive rats gather together typical features Placenta 31,439–447. of human chronic left-ventricular dysfunction with preserved ejection fraction. Pai, V., Marshall, A., Hernandez, L., Buckley, A., & Horseman, N. (2009). Altered serotonin JHypertens32,1307–1316. physiology in human breast cancers favors paradoxical growth and cell survival. Matsumura, N., Mandai, M., Miyanishi, M., Fukuhara, K., Baba, T., Higuchi, T., ... Fujii, S. Breast Cancer Res 11,R81. (2006). Oncogenic property of acrogranin in human uterine leiomyosarcoma: Direct Park, K. -S., Sin, P. -J., Lee, D. H., Cha, S. -K., Kim, M. -J., Kim, N. -H., ... Kong, I. D. (2011). evidence of genetic contribution in in vivo tumorigenesis. Clin Cancer Res 12, Switching-on of serotonergic calcium signaling in activated hepatic stellate cells. 1402–1411. WJG 17,164–173. McCorvy, J. D., & Roth, B. L. (2015). Structure and function of serotonin G protein-coupled Paulmann, N., Grohmann, M., Voigt, J. -P., Bert, B., Vowinckel, J., Bader, M., ... Walther, D. J. receptors. Pharmacol Ther 150,129–142. (2009). Intracellular serotonin modulates insulin secretion from pancreatic beta-cells McDevitt, R. A., & Neumaier, J. F. (2011). Regulation of dorsal raphe nucleus function by protein serotonylation. PLoS Biol 7, e1000229. by serotonin autoreceptors: A behavioral perspective. J Chem Neuroanat 41, Pavone, L. M., Rea, S., Trapani, F., De Pasquale, V., Tafuri, S., Papparella, S., & Paciello, O. 234–246. (2012). Role of serotonergic system in the pathogenesis of fibrosis in canine idiopathic McGlashon, J. M., Gorecki, M. C., Kozlowski, A. E., Thirnbeck, C. K., Markan, K. R., Leslie, K. L., inflammatory myopathies. Neuromuscul Disord 22, 549–557. ... Gillum, M. P. (2015). Central serotonergic neurons activate and recruit thermogenic Pelloux, Y., Dilleen, R., Economidou, D., Theobald, D., & Everitt, B. J. (2012). Reduced fore- brown and beige fat and regulate glucose and lipid homeostasis. Cell Metab 21, brain serotonin transmission is causally involved in the development of compulsive 692–705. cocaine seeking in rats. Neuropsychopharmacology 37,2505–2514. Meltzer, H. Y. (2013). Update on typical and atypical antipsychotic drugs. Annu Rev Med Pennanen, L., Van Der Hart, M., Yu, L., & Tecott, L. H. (2013). Impact of serotonin (5-HT)2C 64,393–406. receptors on executive control processes. Neuropsychopharmacology 38,957–967. Merzak, A., Koochekpour, S., Fillion, M. P., Fillion, G., & Pilkington, G. F. (1996). Mol Brain Peroutka, S. J., Lebovitz, R. M., & Snyder, S. H. (1981). Two distinct central serotonin recep- Res 41,1–7. tors with different physiological functions. Science 212,827–829. Mialet-Perez, J., D'Angelo, R., Villeneuve, C., Ordener, C., Negre-Salvayre, A., Parini, A., & Pitychoutis, P., Belmer, A., Moutkine, I., Adrien, J., & Maroteaux, L. (2015). Mice lacking the Vindis, C. (2012). Serotonin 5-HT2A receptor-mediated hypertrophy is negatively serotonin Htr2B receptor gene present an antipsychotic-sensitive schizophrenic-like regulated by caveolin-3 in cardiomyoblasts and neonatal cardiomyocytes. J Mol Cell phenotype. Neuropsychopharmacology 40,2764–2773. Cardiol 52,502–510. Pockros, L. A., Pentkowski, N. S., Conway, S. M., Ullman, T. E., Zwick, K. R., & Neisewander, J. Millan, M. J., Gobert, A., Lejeune, F., Dekeyne, A., Newman-Tancredi, A., Pasteau, V., ... L. (2012). 5-HT2A receptor blockade and 5-HT2C receptor activation interact to reduce Cussac, D. (2003). The novel melatonin agonist agomelatine (S20098) is an antago- cocaine hyperlocomotion and Fos protein expression in the caudate-putamen. nist at 5-hydroxytryptamine2C receptors, blockade of which enhances the activity Synapse 66,989–1001. of frontocortical dopaminergic and adrenergic pathways. J Pharmacol Exp Ther 306, Porter, R. H., Benwell, K. R., Lamb, H., Malcolm, C. S., Allen, N. H., Revell, D. F., ... Sheardown, 954–964. M. J. (1999). Functional characterization of agonists at recombinant human 5-HT2A, Miyazaki, M., Higashi, Y., Goto, C., Chayama, K., Yoshizumi, M., Sanada, H., ... Sueda, T. 5-HT2B and 5-HT2C receptors in CHO-K1 cells. Br J Pharmacol 128,13–20. (2007). Sarpogrelate hydrochloride, a selective 5-HT2A antagonist, improves vascular Porvasnik, S. L., Germain, S., Embury, J., Gannon, K. S., Jacques, V., Murray, J., ... Al-Mousily, function in patients with peripheral arterial disease. J Cardiovasc Pharmacol 49, F. (2010). PRX-08066, a novel 5-hydroxytryptamine receptor 2B antagonist, reduces 221–227. monocrotaline-induced pulmonary arterial hypertension and right ventricular hyper- Monassier, L., Laplante, M. A., Jaffre, F., Bousquet, P., Maroteaux, L., & de Champlain, J. trophy in rats. J Pharmacol Exp Ther 334,364–372. (2008). Serotonin 5-HT2B receptor blockade prevents reactive oxygen species- Pritchett, D. B., Bach, A. W., Wozny, M., Taleb, O., Dal Toso, R., Shih, J. C., & Seeburg, P. H. induced cardiac hypertrophy in mice. Hypertension 52,301–307. (1988). EMBO J 7,4135–4140. Morita, K., Arimochi, H., Itoh, H., & Her, S. (2006). Possible involvement of 5alpha-reduced Quesseveur, G., Repérant, C., David, D. J., Gardier, A. M., Sanchez, C., & Guiard, B. P. neurosteroids in adrenergic and serotonergic stimulation of GFAP gene expression in (2013). 5-HT₂a receptor inactivation potentiates the acute antidepressant-like rat C6 glioma cells. Brain Res 1085,49–56. activity of escitalopram: Involvement of the noradrenergic system. Exp Brain Muntasir, H. A., Rashid, M., Komiyama, T., Kawakami, J., & Nagatomo, T. (2006). Identifi- Res 226, 285–295. cation of amino acid residues important for sarpogrelate binding to the human Rashid, M., Manivet, P., Nishio, H., Pratuangdejkul, J., Rajab, M., Ishiguro, M., ... Nagatomo, 5-hydroxytryptamine2A serotonin receptor. J Pharmacol Sci 102,55–63. T. (2003). Identification of the binding sites and selectivity of sarpogrelate, a novel 5- Murnane, K. S., Winschel, J., Schmidt, K. T., Stewart, L. M., Rose, S. J., Cheng, K., ... Howell, L. HT2 antagonist, to human 5-HT2A,5-HT2B and 5-HT2C receptor subtypes by molecular L. (2013). Serotonin 2A receptors differentially contribute to abuse-related effects of modeling. Life Sci 73,193–207. cocaine and cocaine-induced nigrostriatal and mesolimbic dopamine overflow in Reavill, C., Kettle, A., Holland, V., Riley, G., & Blackburn, T. P. (1999). Attenuation of nonhuman primates. J Neurosci 33, 13367–13374. haloperidol-induced catalepsy by a 5-HT2C receptor antagonist. Br J Pharmacol 126, Murray, K. C., Stephens, M. J., Ballou, E. W., Heckman, C. J., & Bennett, D. J. (2011). Moto- 572–574. neuron excitability and muscle spasms are regulated by 5-HT2B and 5-HT2C receptor Ren, S., Qian, S., Wang, W., Liu, J., & Liu, P. (2013). Prospective study of sarpogrelate hydro- activity. J Neurophysiol 105,731–748. chloride on patients with arteriosclerosis obliterans. Ann Thorac Cardiovasc Surg 19, Nabeshima, T., Ishikawa, K., Yamaguchi, K., Furukawa, H., & Kameyama, T. (1987). 30–34. Phencyclidine-induced head-twitch responses as 5-HT2 receptor-mediated behavior Robiolio, P. A., Rigolin, V. H., Wilson, J. S., Harrison, J. K., Sanders, L. L., Bashore, T. M., & in rats. Neurosci Lett 76,335–338. Feldman, J. M. (1995). Carcinoid heart disease. Correlation of high serotonin levels Nebigil, C. G., Etienne, N., Messaddeq, N., & Maroteaux, L. (2003). Serotonin is a novel sur- with valvular abnormalities detected by cardiac catheterization and echocardiogra- vival factor of cardiomyocytes: Mitochondria as a target of 5-HT2B-receptor signaling. phy. Circulation 92,790–795. FASEB J 17,1373–1375. Rocha, B. A., Goulding, E. H., O'Dell, L. E., Mead, A. N., Coufal, N. G., Parsons, L. H., & Tecott, Nebigil, C. G., Hickel, P., Messaddeq, N., Vonesch, J. -L., Douchet, M. -P., Monassier, L., ... L. H. (2002). Enhanced locomotor, reinforcing, and neurochemical effects of cocaine Maroteaux, L. (2001). Ablation of serotonin 5-HT2B receptors in mice leads to abnor- in serotonin 5-hydroxytryptamine 2C receptor mutant mice. J Neurosci 22, mal cardiac structure and function. Circulation 103, 2973–2979. 10039–10045. L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36 35

Rosenzweig-Lipson, S., Zhang, J., Mazandarani, H., Harrison, B. L., Sabb, A., Sabalski, J., ... agonist: In vitro and in vivo pharmacological characterization. J Pharmacol Exp Ther Dunlop, J. (2006). Antiobesity-like effects of the 5-HT2C receptor agonist WAY- 325,577–587. 161503. Brain Res 1073-1074,240–251. Tiihonen, J., Lonnqvist, J., Wahlbeck, K., Klaukka, T., Niskanen, L., Tanskanen, A., & Haukka, Roth, B. L. (2007). Drugs and valvular heart disease. N Engl J Med 356,6–9. J. (2009). 11-year follow-up of mortality in patients with schizophrenia: A Rothman, R. B., Baumann, M. H., Savage, J. E., Rauser, L., McBride, A., Hufeisen, S. J., & Roth, population-based cohort study (FIN11 study). Lancet 374,620–627. B. L. (2000). Evidence for possible involvement of 5-HT2B receptors in the cardiac Tschentscher, F., Husing, J., Holter, T., Kruse, E., Dresen, I. G., Jockel, K. H., ... Zeschnigk, M. valvulopathy associated with fenfluramine and other serotonergic medications. (2003). Tumor classification based on gene expression profiling shows that uveal Circulation 102, 2836–2841. melanomas with and without monosomy 3 represent two distinct entities. Cancer Ruddell, R. G., Oakley, F., Hussain, Z., Yeung, I., Bryan-Lluka, L. J., Ramm, G. A., & Mann, D. A. Res 63,2578–2584. (2006). A role for serotonin (5-HT) in hepatic stellate cell function and liver fibrosis. Tsuchioka, M., Takebayashi, M., Hisaoka, K., Maeda, N., & Nakata, Y. (2008). Serotonin Am J Pathol 169,861–876. (5-HT) induces glial cell line-derived neurotrophic factor (GDNF) mRNA expression Russell, A., Banes, A., Berlin, H., Fink, G. D., & Watts, S. W. (2002). 5-Hydroxytryptamine2B via the transactivation of fibroblast growth factor receptor 2 (FGFR2) in rat C6 glioma receptor function is enhanced in the N(omega)-nitro-L-arginine hypertensive rat. cells. J Neurochem 106,244–257. J Pharmacol Exp Ther 303,179–187. van Gils, W., Lodder, E. M., Mensink, H. W., Kiliç, E., Naus, N. C., Brüggenwirth, H. T., ... de Salomon, L., Lanteri, C., Godeheu, G., Blanc, G., Gingrich, J., & Tassin, J. P. (2007). Paradox- Klein, A. (2008). Gene expression profiling in uveal melanoma: Two regions on 3p ical constitutive behavioral sensitization to amphetamine in mice lacking 5-HT2A related to prognosis. Invest Ophthalmol Vis Sci 49, 4254–4262. receptors. Psychopharmacology 194,11–20. Varela, M. J., Brea, J., Loza, M. I., Maldonado, R., & Robledo, P. (2011). Sensitization Saltzman, A. G., Morse, B., Whitman, M. M., Ivanshchenko, Y., Jaye, M., & Felder, S. (1991). to MDMA locomotor effects and changes in the functionality of 5-HT(2A)andD₂ Cloning of the human serotonin 5-HT2 and 5-HT1C receptor subtypes. Biochem receptors in mice. Behav Pharmacol 22,362–369. Biophys Res Commun 181,1469–1478. Vickers, S. P., & Dourish, C. T. (2004). Serotonin receptor ligands and the treatment of Sarrouilhe, D., Clarhaut, J., Defamie, N., & Mesnil, M. (2015). Serotonin and cancer: What is obesity. Curr Opin Investig Drugs 5,377–388. the link? Curr Mol Med 15,62–77. Vickers, S. P., Clifton, P. G., Dourish, C. T., & Tecott, L. H. (1999). Reduced satiating effect of Schellekens, H., De Francesco, P. N., Kandil, D., Theeuwes, W. F., Mccarthy, T., van Oeffelen, d-fenfluramine in serotonin 5-HT2C receptor mutant mice. Psychopharmacology 143, W. E. P. A., ... Cryan, J. F. (2015). Ghrelin's orexigenic effect is modulated via a seroto- 309–314. nin 2C receptor interaction. ACS Chem Neurosci. Vickers, S. P., Dourish, C. T., & Kennett, G. A. (2001). Evidence that hypophagia induced by Schmuck, K., Ullmer, C., Engels, P., & Lübbert, H. (1994). Cloning and functionnal charac- d-fenfluramine and d-norfenfluramine in the rat is mediated by 5-HT2C receptors. terisation of the human 5-HT2B serotonin receptor. FEBS Lett 342,85–90. Neuropharmacology 41,200–209. Schmuck, K., Ullmer, C., Kalkman, H., Probst, A., & Lübbert, H. (1996). Activation of men- Vinals, X., Moreno, E., Lanfumey, L., Cordomi, A., Pastor, A., de La Torre, R., ... Robledo, P. ingeal 5-HT2B receptors: An early step in the generation of migraine headache? Eur J (2015). Cognitive impairment induced by Delta9-tetrahydrocannabinol occurs Neurosci 8,959–967. through heteromers between cannabinoid CB1 and serotonin 5-HT2A receptors. Schraenen, A., Lemaire, K., de Faudeur, G., Hendrickx, N., Granvik, M., Van Lommel, L., ... PLoS Biol 13, e1002194. Schuit, F. (2010). Placental lactogens induce serotonin biosynthesis in a subset of Vindis, C., D'Angelo, R., Mucher, E., Negre-Salvayre, A., Parini, A., & Mialet-Perez, J. (2010). mouse beta cells during pregnancy. Diabetologia 53,2589–2599. Essential role of TRPC1 channels in cardiomyoblasts hypertrophy mediated by 5-HT2A Setola, V., Dukat, M., Glennon, R. A., & Roth, B. L. (2005). Molecular determinants for serotonin receptors. Biochem Biophys Res Commun 391,979–983. the interaction of the valvulopathic anorexigen norfenfluramine with the 5-HT2B Visconti, R. P., Ebihara, Y., LaRue, A. C., Fleming, P. A., McQuinn, T. C., Masuya, M., ... Drake, receptor. Mol Pharmacol 68,20–33. C. J. (2006). An in vivo analysis of hematopoietic stem cell potential: Hematopoietic Setola, V., Hufeisen, S. J., Grande-Allen, K. J., Vesely, I., Glennon, R. A., Blough, B., ... origin of cardiac valve interstitial cells. Circ Res 98,690–696. Roth, B. L. (2003). 3,4-Methylenedioxymethamphetamine (MDMA, “ecstasy”) Wacker, D., Wang, C., Katritch, V., Han, G. W., Huang, X. P., Vardy, E., ... Stevens, R. C. induces fenfluramine-like proliferative actions on human cardiac valvular inter- (2013). Structural features for functional selectivity at serotonin receptors. Science stitial cells in vitro. Mol Pharmacol 63,1223–1229. 340,615–619. Shahid, M., Walker, G. B., Zorn, S. H., & Wong, E. H. F. (2009). Asenapine: A novel psycho- Wainscott, D. B., Cohen, M. L., Schenck, K. W., Audia, J. E., Nissen, J. S., Baez, M., ... Nelson, D. pharmacologic agent with a unique human receptor signature. JPsychopharmacol23, L. (1993). Pharmacological characteristics of the newly cloned rat 5-hydroxytrypta- 65–73. mine 2F receptor. Mol Pharmacol 43,419–426. Shapiro, D. A., Renock, S., Arrington, E., Chiodo, L. A., Liu, L. X., Sibley, D. R., ... Mailman, R. Wainscott, D. B., Lucaites, V. L., Kursar, J. D., Baez, M., & Nelson, D. L. (1996). Pharmacologic (2003). Aripiprazole, a novel atypical antipsychotic drug with a unique and robust characterization of the human 5-hydroxytryptamine2B receptor: Evidence for species pharmacology. Neuropsychopharmacology 28,1400–1411. differences. J Pharmacol Exp Ther 276,720–727. Sharma, S. K., Del Rizzo, D. F., Zahradka, P., Bhangu, S. K., Werner, J. P., Kumamoto, H., ... Wang, C., Jiang, Y., Ma, J., Wu, H., Wacker, D., Katritch, V., ... Xu, H. E. (2013). Structural Dhalla, N. S. (2001). Sarpogrelate inhibits serotonin-induced proliferation of porcine basis for molecular recognition at serotonin receptors. Science 340,610–614. coronary artery smooth muscle cells: Implications for long-term graft patency. Ann Watanabe, H., Nakano, T., Saito, R., Akasaka, D., Saito, K., Ogasawara, H., ... Aso, H. (2016). Thorac Surg 71,1856–1864 (discussion 1865). Serotonin improves high fat diet induced obesity in mice. PLoS One 11, e0147143. Siuciak, J. A., Chapin, D. S., McCarthy, S. A., Guanowsky, V., Brown, J., Chiang, P., ... Iredale, Watanabe, T., Pakala, R., Katagiri, T., & Benedict, C. R. (2001). Serotonin potentiates angio- P. A. (2007). CP-809,101, a selective 5-HT2C agonist, shows activity in animal models tensin II-induced vascular smooth muscle cell proliferation. Atherosclerosis 159, of antipsychotic activity. Neuropharmacology 52,279–290. 269–279. Smith, S. R., Weissman, N. J., Anderson, C. M., Sanchez, M., Chuang, E., Stubbe, S., ... Group B Watts, S. W., & Fink, G. D. (1999). 5-HT2B-receptor antagonist LY-272015 is antihyperten- M a L f O a O M B S (2010). Multicenter, placebo-controlled trial of lorcaserin for sive in DOCA-salt-hypertensive rats. Am J Phys 276, H944–H952. weight management. NEnglJMed363,245–256. Watts, S. W., Baez, M., & Webb, R. C. (1996). The 5-hydroxytryptamine2B receptor and 5- Söhle, J., Machuy, N., Smailbegovic, E., Holtzmann, U., Grönniger, E., Wenck, H., ... HT receptor signal transduction in mesenteric arteries from deoxycorticosterone Winnefeld, M. (2012). Identification of new genes involved in human adipogenesis acetate-salt hypertensive rats. J Pharmacol Exp Ther 277, 1103–1113. and fat storage. PLoS One 7,e31193. Weir, E. K., Obreztchikova, M., & Hong, Z. (2008). Fenfluramine: Riddle or Rosetta stone? Soll, C., Jang, J. H., Riener, M. -O., Moritz, W., Wild, P. J., Graf, R., & Clavien, P. -A. (2010). Eur Respir J 31,232–235. Serotonin promotes tumor growth in human hepatocellular cancer. Hepatology 51, Westbroek, I., van Der Plas, A., de Rooij, K. E., Klein-Nulend, J., & Nijweide, P. J. (2001). 1244–1254. Expression of serotonin receptors in bone. J Biol Chem 276,28961–28968. Soll, C., Riener, M. -O., Oberkofler, C. E., Hellerbrand, C., Wild, P. J., Deoliveira, M. L., & Wienecke, J., Westerdahl, A. -C., Hultborn, H., Kiehn, O., & Ryge, J. (2010). Global gene Clavien, P. -A. (2012). Expression of serotonin receptors in human hepatocellular expression analysis of rodent motor neurons following spinal cord injury associates cancer. Clin Cancer Res 18,5902–5910. molecular mechanisms with development of postinjury spasticity. J Neurophysiol Sonier, B., Arseneault, M., Lavigne, C., Ouellette, R. J., & Vaillancourt, C. (2006). The 5-HT2A 103,761–778. serotoninergic receptor is expressed in the MCF-7 human breast cancer cell line and Xia, Z., Gray, J. A., Compton-Toth, B. A., & Roth, B. L. (2003a). A direct interaction of PSD-95 reveals a mitogenic effect of serotonin. Biochem Biophys Res Commun 343,1053–1059. with 5-HT2A serotonin receptors regulates signal transduction and receptor traffick- Stefulj, J., Jernej, B., Cicin-Sain, L., Rinner, I., & Schauenstein, K. (2000). mRNA expression ing. JBiolChem278,21901–21908. of serotonin receptors in cells of the immune tissues of the rat. Brain Behav Immun 14, Xia, Z., Hufeisen, S. J., Gray, J. A., & Roth, B. L. (2003b). The PDZ-binding domain is essential 219–224. for the dendritic targeting of 5-HT2A serotonin receptors in cortical pyramidal Sumara, G., Sumara, O., Kim, J. K., & Karsenty, G. (2012). Gut-derived serotonin is a mul- neurons in vitro. Neuroscience 122,907–920. tifunctional determinant to fasting adaptation. Cell Metab 16,588–600. Xu, Y., Jones, J. E., Kohno, D., Williams, K. W., Lee, C. E., Choi, M. J., ... Elmquist, J. K. (2008). Sun, Y. M., Su, Y., Jin, H. B., Li, J., & Bi, S. (2011). Sarpogrelate protects against high glucose- 5-HT2CRs expressed by pro-opiomelanocortin neurons regulate energy homeostasis. induced endothelial dysfunction and oxidative stress. Int J Cardiol 147,383–387. Neuron 60,582–589. Svejda, B., Kidd, M., Giovinazzo, F., Eltawil, K., Gustafsson, B. I., Pfragner, R., & Modlin, I. M. Yabanoglu, S., Akkiki, M., Seguelas, M. H., Mialet-Perez, J., Parini, A., & Pizzinat, N. (2009). (2010). The 5-HT2B receptor plays a key regulatory role in both neuroendocrine Platelet derived serotonin drives the activation of rat cardiac fibroblasts by 5-HT2A tumor cell proliferation and the modulation of the fibroblast component of the receptors. J Mol Cell Cardiol 46,518–525. neoplastic microenvironment. Cancer 116,2902–2912. Yadav, V. K., Oury, F., Suda, N., Liu, Z. -W., Gao, X. -B., Confavreux, C., ... Karsenty, G. (2009). Takahara, M., Kaneto, H., Katakami, N., Iida, O., Matsuoka, T. A., & Shimomura, I. (2014). A serotonin-dependent mechanism explains the leptin regulation of bone mass, Effect of sarpogrelate treatment on the prognosis after endovascular therapy for appetite, and energy expenditure. Cell 138,976–989. critical limb ischemia. Heart Vessel 29,563–567. Yamada, K., Niki, H., Nagai, H., Nishikawa, M., & Nakagawa, H. (2012). Serotonin potenti- Takishita, E., Takahashi, A., Harada, N., Yamato, M., Yoshizumi, M., & Nakaya, Y. (2004). ates high-glucose-induced endothelial injury: The role of serotonin and 5-HT(2A) Effect of sarpogrelate hydrochloride, a 5-HT2 blocker, on insulin resistance in Otsuka receptors in promoting thrombosis in diabetes. J Pharmacol Sci 119,243–250. Long–Evans Tokushima fatty rats (OLETF rats), a type 2 diabetic rat model. Yang, M., Li, K., Ng, P. C., Chuen, C. K., Lau, T. K., Cheng, Y. S., ... Fok, T. F. (2007). Promoting J Cardiovasc Pharmacol 43,266–270. effects of serotonin on hematopoiesis: Ex vivo expansion of cord blood CD34+ stem/ Tanaka, K., Hirai, T., Ishibashi, Y., Izumo, N., & Togari, A. (2015). Modulation of osteoblast progenitor cells, proliferation of bone marrow stromal cells, and antiapoptosis. Stem differentiation and bone mass by 5-HT2A receptor signaling in mice. Eur J Pharmacol Cells 25,1800–1806. 762,150–157. Ye, J. Y., Liang, E. Y., Cheng, Y. S., Chan, G. C. F., Ding, Y., Meng, F., ... Yang, M. (2014). Sero- Thomsen, W. J., Grottick, A. J., Menzaghi, F., Reyes-Saldana, H., Espitia, S., Yuskin, D., ... tonin enhances megakaryopoiesis and proplatelet formation via p-Erk1/2 and F-actin Behan, D. (2008). Lorcaserin, a novel selective human 5-hydroxytryptamine2C reorganization. Stem Cells 32,2973–2982. 36 L. Maroteaux et al. / Pharmacology & Therapeutics 170 (2017) 14–36

Zhang, Y., Yang, Y., Chen, L., & Zhang, J. (2014). Expression analysis of genes and monocrotaline-induced pulmonary arterial hypertension in rats. Eur J Pharmacol pathways associated with liver metastases of the uveal melanoma. BMC Med 670,195–203. Genet 15,29. Zsippai, A., Szabó, D. R., Szabó, P. M., Tömböl, Z., Bendes, M. R., Nagy, Z., ... Igaz, P. (2011). Zopf,D.A.,Neves,L.A.A.d.,Nikula,K.J.,Huang,J.,Senese,P.B.,&Gralinski,M.R. mRNA and microRNA expression patterns in adrenocortical cancer. Am J Cancer Res 1, (2011). C-122, a novel antagonist of serotonin receptor 5-HT(2B), prevents 618–628.